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By Greg & Helen Sosna We often get asked about what kind of rechargeable AA and AAA batteries are best to buy and which charger to use. This short article will only cover rechargeable batteries currently readily available on the market in NZ. I will not cover the non-rechargeable batteries, or batteries that are used in the outer space... ;-) Please use this article as a guide, not as a bible - and do your research too before buying!!!
There are pretty much two main kinds of rechargeable batteries available: - NiCd - Nickel Cadmium - NiMH - Nickel Metal Hydride NiCd were first out on the mass-market, prior to 2000 these would be the only ones you'd be looking at. For that reason, NiCd are still most popular around, however, they're quickly being replaced with NiMH. NiMH can store much more charge (3-4 times) and they don't have what's called "memory-effect". Memory effect is a simple explanation of the chemical property that requires the cell to be completely discharged before being charged, otherwise the cell will "loose" its capacity. That process is usually irreversible. One good thing about NiCd-s is that once charged, they do not loose (aka leak) charge, a good NiCd cell can keep its charge for one year and even more. They're perfect for "cyclical" uses, with the right parameters! (in fact they're used in space, when they know how much solar charge they'll get in a day, then it gets completely discharged during night - of course, calculated very carefully!) NiCDs are best charged with smaller current meaning longer charge times. NiMH batteries, do not have the memory effect, which means you can charge anytime, including top-up. It's not advantageous at all discharging the battery completely. In fact there's some argument that proves that it's best to charge NiMHs as soon as you get near to a charger. But they do leak (even when there's nothing plugged in!) A fully charged NiMH will keep its full charge for max 1 week, and after 2 months it will be completely discharged. For most electronics applications today (GPS, Digital Camera...), I recommend NiMH batteries. For torches, bike lights I recommend NiCD. They come in various sizes AAA, AA, C, D Note that not all devices will be compatible with rechargeable batteries. Some electronics might not run on them at all (I used to have an old CD player that just didn't go). Reason for this is that non-rechargeable batteries are 1.5V (some are even 1.7V!!! - eg. panasonic oxyride), where the rechargeable cells are 1.2V and very rarely 1.25V (you got to pay $$$ for that extra 0.05V!!!! - it does make a difference, but I don't have any 1.25V myself at the moment). That should not worry you much, but keep that in mind. Some devices (our GPS garmin geko does - in setup options) ask you what kind of battery are you using, so that they can measure its charge more appropriately, so check these GPS manuals! Capacity is measured in Ah - which stands for Ampero-hours. 1Ah means that a device can eat 1A for 1h. Roughly!!! Your car battery is about 20-40Ah. Unfortunately (well...) AAA and AA batteries capacity is measured in mAh - mili ampero hours. The most you can buy is 2500mAh these days, of course they are 3200mAh, but you'll have to make some calculations. It's easy - eg. 2500mAh is double capacity of 1250mAh and it will last twice as long. Your cheap supermarked noname non-rechargeable battery is about 1700mAh (but since it's 1.5V, it'll behave like 2200mAh), an expensive Energiser will feel like a 4000mAh, and panasonic oxyride (due to its high voltage) will feel like 7000mAh. Note that Panasonic Oxyride shouldn't be used in torches. And some electronics MIGHT get damaged (never heard, but they're 1.7V... that's significantly more than specifications)... Anyways... Chargers - they're easy to work out too. if you buy a charger that charges 1.2V at 100mA, then it will take 25 hours to charge 2500mAh battery, you probably need to add 10% just to make sure, so about 28 hours. A charger that is rated 1.2V 1500mA, will charge 2500mAh battery in roughly 2 hours. Batteries will get damaged when overcharged, so it's smart to buy a charger with circuitry that will prevent overcharging. That's a difference between $20 charger and $70 charger... sorry~!!! One more thing, faster you go, bigger the mess... I mean faster you charge a rechargeable battery, then faster you will throw it away. They usually have ratings saying that it will last 1000 full charges, the little asterisk is that you will need to charge with 200mA current, which is of course ridiculous. From experience, I found that they usually last for around 200 charges at 2000mA charging. Which strikes a good balance between cost of them (still waaaaaaaay cheaper than buying new batteries) and time that it takes to charge. Since AAA batteries are of smaller capacity (700-1200mAh) than AA, the chargers use smaller current to charge AAA's than AA's to protect their lifetime. Just before I make final recommendations, keep in mind there are also the following types of rechargeable batteries: - Lead - car batteries - LiIon - Lithium - used mostly in electronics, mobile phones, laptops - superior to NiMH (smaller, lighter) - many many more... There are also "15 minute chargers" available from Varta I think, they are around 2000mAh, and charge with 6A current, these batteries will last for around 100 charges or less. They are also quite expensive, and are not considered main-stream. But if you're happy to pay for convenience, these are the best in its range. RECOMMENDATION: batteries for GPS: AAA NiMH 900mAh+ (they're often on special, and reduced price for multi-packs... it could be good idea to hold on buying bulk till there's a special...) Charger: for NiMH charging: AA @ 1.5-2A, AAA @ 0.5-1A make sure you have triple voltage 110/240V power supply and 12V car cable for them too - very handy!!! dse jaycar1 jaycar2 jaycar3 (there are new models at jaycar, just search!!!) USB chargers (eg. jaycar3) are quite popular, but they usually take longer than using power/12V to charge and also not all computers will like them... but they are convenient! |
