Volts, Batteries and Stuff

Diving, like so much of life, now relies on electric power, particularly battery power, its worth considering some of the problems this engenders before setting off on any travel. Yes, even travel within the UK is worth thinking about for some of the issues, but flying brings a whole host of potential new difficulties. Green issues also surround batteries.

Airlines are confused about batteries, some say leave in equipment but then on check-in insist they are removed. Some insist spares are packed in baggage, other in carry on, sometimes changing their mind at check-in. Some try to set limits on total numbers particularly with lithium batteries but others also. At least pack spares so it is impossible to short circuit or crush them, the special battery holder packs might just get you through check-in with an explanation of why you need so many batteries.

If you don't want a lot of details the quick summary is:
1. Use rechargeable NiMH (nickel-metal hydride) batteries where possible.
2. Use a microprocessor controlled "smart" charger for charging those batteries.
3. Carry spare batteries on their own in small strong purpose made plastic boxes with nothing metallic available to short them. Lithium "coin" cells keep in original packaging.
4. Leave "in use" batteries in the computer, camera, etc. but make sure it can't be accidentally turned on (applies particularly to torches).
5. Keep and use batteries as sets, don't mix.
6. Carry a multiway extension lead (4 + sockets) which has surge protection.
7. Non-rechargeable lithium are a good emergency set but expensive.
8. Rechargeable Lithium-ion chargers need to be checked for voltage compatibility
9. Don't bother with the alkaline's except in exceptional circumstances as they don't offer much performance particularly for high drain applications though they may be desired by some for backup torches. The old style zinc-carbon can be left on the shelf unsold.
10. Bring home old batteries for disposal.


1. Battery Power

Found in all sort of places from the laptop, to camera and flash, to MP3 player or even your dive computer. It's best to try and use rechargeable batteries in many of these situations but not all. So why rechargeable batteries?
a. Much kinder on the environment than disposing of lots of disposable ones.
b. Ultimately its also kinder on your wallet.

2. Mains power

Great if you have it, sometimes essential
Not always found. If found may be the wrong sort :-)

What do we mean Mains Power the Wrong Sort?

The mains voltage, frequency and plug types vary around the world and you are going to be dependent on this. In the UK we nominally have 240 volts at 50 Hz (that's the frequency or cycles bit) and you know the plug. Other countries will fall into two general bands with voltage:

1. Those with 100 to 120 volts and (mainly North America)
2. Those with 200 to 240 volts.

Frequency can be either 50 or 60 Hz or on liveaboards almost anything.

Liveaboards can have widely fluctuating supplies (volts and frequency) but usually something. Caution it just might be for limited hours a day. Fluctuations can put a lot of strain on battery chargers and many burn out, can you cope with a dead charger?
Day boats may not have any supply. Be prepared for your full days power supply needs.
Land - it all depends on where you are :-( . Ask some questions! Check!

The mains power which is of concern here is primarily going to be needed for recharging those rechargeable batteries. Its also just as important if you want to plug in that hair dryer, electric razor, big sound system, laptop or portable fridge for the beer. One of the last things you want is to find you can't do it.

Tip: Adapters to the various plug types for the mains are available singly or as expensive multi county kits but if you are going to have a bit of time at your destination an alternative is to buy a plug locally. So, a useful item to carry can be a surge protected extension lead with multiple outlets and the original plug can simply be replaced with the local one. It's easy to find a group of you needing to charge torches and only one power point in an inaccessible location so the multiple outlets come in handy.
See Mains

In your hotel you might well find a shaver point. Great for shaving, probably fine for a small battery charger but it's designed for low current and certainly will not power that hair dryer and maybe not even a larger battery charger such as with a big torch. That multiway socket with lead can help to put your sockets where it's convenient.

If you have something like a big torch which needs a long charging time do you have the time for it to fully charge? On that liveaboard or eco-lodge with generators only running during the day (so people can sleep!) backup alternatives might be worth having with you.



Mains:

So why are the mains power characteristics important to you?

If you are plugging in that hair dryer, etc. you don't want it to immediately burn out! The same applies to battery chargers and other portable equipment using adapters to power them.


Chargers For Batteries generally need mains supply but some will also run from a car battery. Better battery chargers now are often electronic and may be self regulating, but some still use transformers which are heavier.

Transformers or mains adapters, often come with specific items of equipment but more universal ones might be appropriate if you you are taking equipment needing more power. These can change the voltage but not the frequency and they may themselves only be single frequency and single input voltage. If operated at the wrong frequency they can overheat and burn out! If the voltage is wrong it won't be a matter of "can" they will overheat and can burn out spectacularly if the voltage is too high (if you switched them to 110 volts overseas remember to switch back on returning home) and possibly if too low.

Tip: Check your adapters, it should give specifications on it! It may be possible to set its input voltage, it may handle 50-60 Hz, it may be electronic and automatically adapt within some given ranges. If it's wrong alternatives might be possible and one of the things to watch for is the current rating in mAh (milli amp hours, or if its a high power appliance in Amp hours). It must be high enough to comfortably handle your equipment. With electronic equipment the adapters are often reducing the voltage (check your equipment specifications) and electronic ones are more likely to be self adapting to the input volts and frequency but the plug which connects to your equipment might be a custom design and not easily replaced. The subject is too wide to cover fully here but it needs to be considered before you leave. Sometimes, if you are going to a larger city overseas and have time, buying the correct mains adapter locally can be a good option but if it's a bit specialised it may need to be ordered. Check and recheck, what options you have!

Caution Some adapters, appliances, need an earth connection not all overseas sockets will have an earth and your equipment can be "live" (can give you a shock). Try to find adapters not needing an earth (3 pin) connection.

Chargers:


Rechargeable batteries need to be recharged, Chargers:
As important as the batteries are the chargers, maybe even more important. If you are travelling a long way, want to get that picture or see inside the cave you will be depending on these portable power sources! A good charger can make that difference.

NiMH chargers are the most difficult. The charging effect is exothermic, the battery warms up. The voltage change (the minus delta V/ delta t bump) at the end of charge is very small and false changes can occur so voltage detection only is not recommended as a method to stop at full charge. NiMH batteries can be easily damaged by overcharging. The cheapest chargers will trickle charge at 10% of rated capacity per hour for 35% more than the rated capacity - yes, best to calculate this and time the charging, and it assumes a nearly discharged cell, more simply time should not be more than 12-15 hours. These are the charges often sold in general retail shops, try and buy better ones which now often cost no more but need more knowledgeable staff to sell them.

More sophisticated chargers now use a microprocessor to monitor voltage as well as time and temperature. The best ones do this for each individual battery, others only for sets of two batteries. Try and and buy the ones which do individual batteries as they can also tell you that a single battery is going dead. They give the best battery lives and very short charge times. Fast charging can be done at 100% of rated capacity. For best results and best battery life chargers for NiCd and NiMH are not interchangeable unless they use the temperature rise method to detect a fully charged state.

Confused?

Join the crowd! What to buy in a simple fashion? Rechargeable batteries and their chargers get hotly debated in various circles. Conclusion. NiMH cells are the way to go. Cheap chargers let you down. Good microprocessor controlled charges (sometimes say Delta-V circuitry) for 4 to 8 batteries at a time while treating each single cell individually are now available on the net for under £15 but still buy a backup.

Lithium-ion Charging these chargers are generally specific to the battery as so many different lithium chemistries are in use but will be found particularly for laptop, digital camera and video equipment. On some laptop chargers earthing is required for the charger itself, if not the laptop, and at least some overseas hotels only have two pin sockets (Sharm is my example) which resulted in a slightly "live" laptop. Some of these batteries do have after market chargers available.

NiCd and Lead acid batteries are disappearing from the market for most of our uses at least in travelling but for completeness:

NiCd charging is endothermic, as it charges it cools. This can allow very quick charging with the cooling effect from the endothermic reaction counteracting the joule heating effect of putting a current into it. When a cell is fully charged oxygen starts being generated which causes a lowering of the cell voltage which can be used to detect the end of charge, called the minus delta V/ delta t bump. Most of the "smart" charges use this to stop the charge though temperature changes can be an even more precise way to limit the charge. The cheapest chargers trickle charge for 12-16 hours at low current and will adequately charge a cell from most states but don't leave them on longer as slow damage can be done to the batteries. Faster chargers fall into 2 categories: the simple ones that work in a similar fashion by simply relying on time to stop are only safe if it discharges to a know state before starting the charge time. These typically quote a charge times of 4 to 5 hours.

More sophisticated fast chargers monitor both voltage and possible temperature curves to cut the high charging current. These can charge at 100% battery capacity per hour initially then changing to trickle charging. Trickle charging to maintain charge should be done at 0.04 to 0.06% of capacity per hour and its best to check the charger to see what it put out as some go over this.

Lead acid batteries are fairly tolerant of overcharging and this has lead to some very inexpensive chargers as little regulation is required. The cheapest are a simple transformer and diode for producing an overnight trickle charge but due to the transformer which controls both the voltage and current they are heavy compared to electronic chargers. The voltage can also rise after the battery is fully charged and produce electrolysis, so they should not be used for more than 12-24 hours. Adding a voltage regulator adds little to the cost and now they can be used to maintain a charge state by trickle charging. Adding current limiting to this improves it still further. Fast chargers have still more control circuits and should be able to do a quick charge, 3-5 hours, then maintain it. Always charge lead acid batteries so they can vent to the atmosphere while charging.

Battery Power:

They come in a bewildering range of types and sizes.

Tip: First, its sensible to carry spares, even for the UK.
Tip: Standardise.
Personally, I try where possible and use "AA" size in preference, even to the point of not buying some items because they use something different. OK, for me this size is set because of a camera and flash units but they go into back up torches also.

The "AA" and the "D" seem the most common and in a pinch can probably be bought locally while "C" and "AAA" sizes may be just a little more difficult. The more specialist, though seemingly common, are not necessarily so available. I've been caught needing a "standard camera battery" for a backup camera only to find in a large city with a few hours being killed I couldn't find the right one. So, have spares for dive computer, torch, camera, flash units, O2 analyser, laptop, hearing aid, watch, game, whatever you use :-).

If you use many batteries such as in torches, cameras or flash think of the environment as well as your pocket and use rechargeable ones. They cost a bit more initially but save both money and the environment in the longer run. Whatever batteries you take, bring dead ones home for hazardous waste disposal in an environmentally sound way. Dead batteries do not belong in landfill, particularly not in small tropical islands or isolated resorts.

With any types of batteries keep them together in labelled sets. If your torch/flash/camera uses say 4 keep those 4 together and have a second set of 4. This way an older, weaker battery won't kill fresh, younger ones prematurely. Don't mix makes, mAh capacities and certainly not types.

The NiCd, NiMH and Lithium, can all put out a lot of current, >10 amp when shorted and get hot if discharging at such high rates. In use if one battery in a set is not fully charged or "going off" the others will try and charge it at near that maximum current. This can burn out wiring and the heat generated in the charging battery can damage expensive equipment. This is why airlines become restrictive on batteries, you've probably heard of the burning laptops and mobile phones. This is also a situation where hydrogen gas might be generated from the battery. Water-tight, hence gas tight, aquatic devices must be designed to deal with battery generated hydrogen, usually this is a catalytic converter. These catalysts need replacing if they get wet but replacements seem impossible to find so a once flooded torch or flash might be a potential explosive hazard even if dried out and working.

More on batteries here if you really want more detail More on Batteries

Storage and Transport of those Batteries

Store any battery below 30 C and preferably as cool as possible but above freezing. Remove from equipment if leaving for any extended length of time. Some portable electronic devices place a very low-level drain requirement on their batteries even when in the "off" position. These micro-current loads may be sustaining volatile memory, powering timing/clock circuits or even maintaining switch positions. If this is important exchange and recharge the batteries every 3 or 4 months. If storing devices for protracted periods remove them completely even if it means losing stored settings.

Keep batteries physically protected from sharp objects, hard corners, etc. which can damage them. Particularly keep them away from metal that might cause them to short, for instance never store in a metal box or with loose metal objects. Don't just toss them into the bottom of your bag. I use small plastic specially designed battery boxes for my "AA's" as they protect them, keep them in sets of 4, prevent short circuiting and are cheap at less than a pound a box. Non "AA" I use small plastic food containers with my sets in plastic zip lock bags within these.

Airlines suggest not packing batteries in the luggage to go in the hold, but then sometimes reverse this and insist on it at check-in. Batteries are a complicated subject and airline staff at the check-in level anyway don't necessarily understand all of it. The rulings are partly fire safety but they can also freeze and rupture in the baggage.

Again, don't just toss them into the bottom of a bag where they might find a way of attracting some bit of metal and short. It will be very embarrassing to have your dive kit go up in smoke from a shorted battery overheating. Don't leave them in a high power torch which might accidentally get turned on either, hot bulbs can cause damage. Ideally it is best practice to ship rechargeable batteries in a discharged state which is why the instructions on new equipment say to charge them, but practically this not likely what you will do so at least protect them. The American DOT has passed regulations on Lithium batteries banning them from checked baggage and limiting the number which can be carried which might cause problems for some. It's worth learning enough to be sensible and to understand the implications with batteries, you might need to explain all of this to get on the plane with your kit.

Batteries more

OK, you wanted to know more about batteries, so here goes.
First what is High drain or low drain - what it relates to

Before considering the battery characteristics think of their use. Digital cameras eat batteries, they are high drain. Maybe a bit like the great white shark - fast and ferocious. Electronic flash are also high drain. A small torch with that set of 4 batteries will last for maybe 60 to 80 minutes so is much lower power drain. Think of power per minute; take the total capacity of your batteries (4 x 1800 mAh for my NiMH AAs = 7200 mAh or 7.2 amps) the length of time in active use (like the flash recycling) and the total of this time that your batteries support (say 150 flashes, 4 seconds to recharge each time = 600 seconds, 10 minutes) so my flash draws 0.72 amp per minute. That's about a sixth of what a 1 kw electric heater uses. This is why the type of battery makes such a difference. For instance what they call heavy drain for an alkaline is defined as a use which would discharge the battery within 24 hours, not what we now think of as high drain.

Each major class of battery, each manufacturer has a variety of chemical systems to fine tune a battery cell to specific characteristics. As a user / consumer it can be nearly impossible to tie this down to what you can purchase. Instead all you can look for is total mAh capacity and maybe the different charge / discharge rates (often expressed as a number followed by "C."; higher is better on both these, 1C means one battery capacity per hour, 1/2C is half the capacity per hour).

The battery types or at least the main ones. There are lots more:
A. Primary cells: these are non-rechargeable, i.e. disposable, single use.

1. Zinc-carbon. The old fashioned ones
2. Alkaline. The common ones More Here
3. Lithium. High power, good characteristics. The only type for some applications, good for other jobs but specialised batteries with lithium More Here

B. Rechargeables come in a number of types.
The most common from the diver's perspective will be the lead acid, nickel metal hydride (NiMH), Lithium-ion and the nickel cadmium (NiCd). The rechargeable alkaline has gone from the list since last updating. Rechargeables can deliver more power quicker than alkaline battery cells. If rechargeables are mistreated by wrong charging or draining too flat they can release gas, usually hydrogen which can be explosive! but mistreating will mainly reduce the number of times they can be recharged or the power they can hold.

1. Lead Acid. Car, boat, some torches use these traditional ones More Here
2. Nickel Metal-hydride (NiMH). Ideally the one to go for. More Here
3. Lithium-ion (Li-ion). Common for laptops, digital cameras, mobile phonesMore Here
4. Nickel Cadmium (NiCd). Older type rechargeable. More Here

NiMH and NiCd have some characteristics in common. They both give 1.2 volts, a little lower than the common alkaline cells but they keep this output nearly steady for the complete useful charge life. For most situations these can substitute for the higher voltage primary cells. They can also provide very high current output (a problem if you short them - see note on transporting) so are good for portable instruments, flash units, cameras and other high power uses. They do self discharge so if left for a few weeks before use they should be recharged. Both types have internal mechanisms to control gas release but if shorted (like a sea water flood might do) this can be overwhelmed resulting in a gas explosion. Usually battery containing diving equipment, like torches or flash, have hydrogen catalyst converters and often an explosion release mechanism (much better to blow an end cap off than having the casing explode like a bomb).

Li-ion More Hereactually covers a vast range of battery chemistries with the output voltage ranging from about 3.4 to 3.7 for an individual cell. These are generally found built into multi-cell packages for the specific equipment they will power and the package may have anything from that 3+ volts to 24 volts or more. They are light in weight for the power stored hence use in portable equipment and they don't have the memory effect. They also hold charge longer (low self discharge) than NiMH, but they do deteriorate with age, not number of charge cycles or use i.e. they steadily lose capacity to hold a charge so older batteries will not perform as well as new ones. They are also damaged by too much discharge and heat.
So For best results:
a. Charge little and often
b. Don't deep discharge, i.e. run down flat
c. Occasionally do need to recalibrate
d. Keep cool, even in refrigerator. High temperatures such in overheated car can damage.
e. Only buy when needed not ages in advance (but still need spares)

Primary cell batteries

Dry cells non rechargeable batteries<br> 1. Zinc-carbon or dry cells. These are the least expensive, developed in the 1860's and the only ones readily available till the 1950's. They have a voltage when new and fresh of 1.5 volts which falls with use. They have a relatively low energy density and for best results power can only be taken slowly and intermittently. Not a good choice for much power.

Alkaline non rechargeable batteries
2. Alkaline. They store a lot of power (up to a couple of thousand mAh) which is best delivered at low to moderate discharge rates. They have a voltage of about 1.5 volts when new and fresh and have excellent charge retention during storage. Their internal resistance is less than the zinc-carbon dry cells so they deliver power quicker than those (but much slower than rechargeables) and this power falls off as does voltage with use. With a torch you see this as the light slowly gets dim, with flash units the recycle time gets longer.

The moderate internal resistance does mean start up current is restricted, so bulb filaments in a torch are theoretically less likely to blow when switched on than when high currents are available as from rechargeables (bulb filaments have a low electrical resistance when cold, this increases as they heat up). This is theoretical, I've not had a problem with bulbs blowing when using rechargeable cells in a torch. The good shelf life and low self discharge rates does make these OK for items like dive computers and I do use them in my safety strobe and laser torch as they will continue to work if left. Some divers prefer this type of cell in torches, particularly back up ones, as the slow voltage drop and dimming light acts as a warning that its going to go out. They used to contain traces of mercury which allowed better power characteristics but better brands now have eliminated this so they are not as polluting as they were.

Lithium primary cell batteries
3. Non-rechargeable lithium. These have a voltage of 2.7 to 3.6 volt depending on which of a number of chemistries are used. These voltages remains near constant for their life, the cells have excellent shelf life, low self drain characteristics, and will handle low to moderate current drain. The travelling diver will normally only use these as coin cells in watch and dive computers though some cameras use them. Some digital cameras that take AA size do have special adapters to take them in place of 2 AA size which might be considered for emergency backup but they are expensive. Since the different chemistries give very different characteristics of voltage and current you will need to check specifications carefully. Look for voltage, current, continuous very low drain or pulsed intermittent operational needs.

Lithium / iron disulfide (LiFeS2) are also just called lithium so you need to check voltages to separate the two types. These cells have a voltage of 1.5 volts and can be direct replacements for alkaline and rechargeable battery cells. They have excellent shelf life, low self drain, good high drain power supply and work well over an extended temperature range. They do have the potential to explode if the case is opened in water, put in a fire, put in backwards, or mixed with other battery cell types. They have thermal cut out switches if overheating in use. Power capacity for AA size is around 2900 mAh and they can provide a maximum 2 Amp/min continuous output (i.e. 1.5 minutes to discharge them). If you are transporting more than certain numbers (not high numbers!) special packaging and labelling is required and Transport of Dangerous Goods Regulations may apply - talk to the Department of Transport. Oh, and they are relatively expensive but not prohibitive! Excellent for very cold conditions. Excellent as a backup set for critical emergency equipment such as a portable VHF radio or GPS.

Rechargeable Lead Acid rechargeable batteries
1. Lead acid. These are normally found as batteries made up of a number of cells, the nominal voltage of a cell is 2 volts so 6 cells make up a 12 volt car battery. In the travelling divers kit they will be most often encountered as "sealed" batteries in torches but could be in dive propulsion vehicles and of course boats. They have a high self discharge rate, but are low cost and have a good life cycle and can provide high power delivery. One thing to watch for in any closed container such as a torch is the potential to release hydrogen gas. Catalytic gas recombiners must be used in such closed systems and replaced if you have a flood. Do not store these batteries in a discharged state and due to self discharge top up the charge possibly even monthly, but if they show less than 70% charge than top up as soon as possible. The acid content makes airlines rather reluctant to transport these and only the sealed variety can be flown with (even then airlines might object).

Nickel Metal Hydride rechargeable batteries
3. NiMH. Now the dominant rechargeables and prices can be as low as a good disposable battery. These provide more power and can be charged faster than NiCd cells and they do not have the memory or cadmium considerations so have now supplanted the once main rechargeable NiCd. Without the memory problems these do not need to be discharged completely before recharging. The nearly flat voltage discharge curve, similar to NiCd, starts at 1.4 volts almost immediately drops to 1.2 stays at this level before very rapidly dropping at exhaustion. This means for emergency VHF radios contact could be lost abruptly, for torches light will similarly fail quickly, for battery life indicators on cameras it means the indication is not reliable. They do self discharge, meaning they lose power over time so should be recharged shortly before use but the rate does vary between manufactures.

This type of battery has been developing rapidly over the past 4 to 6 years with improving power and dropping cost. The more powerful ones now will hold 2700 to 3300+ mAh in "AA" size and charge at up to 1C rate. Only 3 years ago the high capacity was in the order of 1800 to 2000+ mAh. Be very careful not to insert a cell in reverse polarity (the "+" and "-" are important), that high power can destroy equipment and batteries can explode. The NiMH batteries are designed with hydrogen gas catalysts inside but this can be overwhelmed if cells are wrongly inserted or if one cell is dying and being charged by others in series (if hydrogen is vented it will do so at over 200 degree C gas temperature!).

One more thing to watch out for is over discharging. Torches particularly can drain a battery pack till it is totally flat. This can put the lest capable cell into reverse charge which shortens its life and can lead to problems with gas (hydrogen) release. Its best to never run a torch till it dies, expensive torches have circuits designed to prevent prevent this.

Tip: battery adapters are available to take an "AA" size and allow it to be used where a "C" or "D" size is otherwise required. This makes one of my "D" cell torches much lighter and with the high power NiMh it lasts as long as using an Alkaline "D" so better for travel. The bulb could be changed to allow for the lower voltage but I haven't bothered as still bright. In another torch the adapters don't make proper contact so they don't work - check yours before depending on it.

Lithium ion rechargeable batteries
4. Li-ion. Lithium ion rechargeable batteries should not be confused with the non rechargeable Lithium batteries! The Li-ion ones are mostly used in specialist appliances such as laptops, cameras or mobile phones in proprietary packs as mentioned earlier but some now are arriving to replace pairs of "AA" cells particularly in point and shoot cameras. One thing to be aware of is they can go into "deep discharge" generally through being left for long periods of time. In this state they may regain capacity by prolonged, meaning days, of recharging but may never recover. Don't leave that laptop unused :-). High temperatures also shortening the number of possible recharge cycles and storing for long periods they do best starting this only partly (40 to 50 %) charged.

Li-ion batteries are much more complicated than the NiMh due to various safety issues with a relatively high failure / recall rate due to these measures. Great batteries for the right applications, not general purpose ones.

Nickel Cadmium rechargeable batteries - now almost history
2. NiCd. Two perceived problems with NiCd cells are the memory effects, much improved in the most recent ones but still present, and the presence of cadmium. The power available has increased with the newer cells, up to about 1300 mAH but lower power ones are much more common and cheaper. Stores selling rechargeable batteries often don't make it clear that it's low power older type NiCd are they are offering at sometime inflated price.

The memory effect manifests itself if a cell is not completely discharged before recharging. Over repeated uses it "learns" to only hold enough power to meet that lower demand. Periodic full discharge cycles will restore most of the capacity, maybe once or twice every 20 uses. Better chargers provide this discharge function. The rate of charging on the standard consumer batteries needs to be of the "trickle" variety normally no more than 100 mAmp. High charge rates are possible on some of the more specialised cells such as used in cordless power tools and in the high power cylindrical cells. These high rate cells need special chargers which should monitor temperature rise and cut off when the rise starts, timing only type high speed chargers are not really adequate and will seriously shorten the cell life.

Cadmium is seen as another problem with these cells, its an environmental pollutant. This may be a little overstated for single cell as its present in very small amounts as a plating on the negative electrode but these cells are scheduled to be banned from 2008. About 2/3rds of the worlds cadmium consumption, some 18,000 tons!, goes into NiCd batteries, of which three quarters is used in small sized consumer cells. Demand for these cells has risen from 1 billion per year in 1990 to 2.5 billion in 2000. Remember, dispose of them when dead in an environmentally friendly fashion.

Some specialist NiCd cells still provide slightly higher discharge rates and some can provide higher temperature operation than the more desirable NiMH but these are becoming niche markets for this older technology.

Rechargeable alkaline batteries - another technology that lost the race
4. Rechargeable alkaline: These have a voltage of 1.5 volts, work well for light power applications particularly intermittent use, have a relatively low self discharge rate and good storage characteristics. These would have been good for emergency VHF radios or GPS units. Power capacity could be at least 2500 mAh so good. They have no memory effects and recharging frequently at only partial drain is the best use practice while more fully discharging reduces the total number of possible charges. They are / were relatively inexpensive (to produce, not necessarily to buy), and are environmentally friendly. But this technology, particularly in the UK, hasn't caught on as it arrived late compared to the NiMH but they may be found. What to watch out for: the chargers for these can NOT be interchanged with those for NiCd or NiMH. a special one is necessary. They need to be charged at constant voltage not constant current.


Charles Stirling