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Carwyn Edwards.
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October 25, 2023 at 9:03 pm #17573
Andrew
SpectatorI have been trying to find out about AA rechargeable batteries. I’m hoping to make sure that my (AA – LED) headtorch works for the longest time possible, should I need to get down the hill after dark. Maybe someone has already found the largest capacity batteries to use and can give advice?
I put brand new 2850 MAH (milliamp hour) batteries in my LED headtorch and on maximum setting I got about 6 hours of useable light. (Other devices may differ, obviously). On some older 2100 MAH batteries, I got 4.5 hours or so. But on some 800 MAH batteries, the light only lasted 1.5 hours ! I imagine these times would be less, in very cold conditions. In a real situation, I could extend the time by using a lower setting and/or rationing the use. This was all crude stuff, but evidently, more MAH means a longer light.
I also found a review of Duracell Plus batteries, (ie non-rechargeable) which the reviewer tested and gave 1442 MAH. So on the face of it the Duracells would only last half as long as the 2850 recharegeables. (ie 3 hours ?) Cheap non-rechargeables seem to avoid quoting their MAH so it is to be feared that they will make a torch come on, but it would go out before you get down to the valley. Plus, I’ve read that when installed in series (as in a torch) the MAH capacity does not increase (although the voltage does). Hence if you mix batteries, you’ll only get the MAH of the lowest rated.
So what I think I have picked up, is to use three of the highest MAH AA-size batteries I can get. Thus I’m interested in 2 things:-
(1) Is anyone using AA batteries bigger than 2850 MAH with good results ?
(2) Is anyone using a headtorch with a single AA battery ? I think such torches will have equivalent battery life (ie same MAH) but with just one battery the LED must run at 1.5 rather than 3.6 to 4.5 volts so what’s the beam like ?Obviously there are USB rechargeables and other sizes of batteries but I have reasons to use AA.
A final thought came from Maria, one of our best mountaineers, some years back. Try actually changing batteries in the dark, wind, and rain !! Better to carry a small emergency second torch rather than spare batteries , she said.
With the clocks about to go back, I’m hoping to “Shine like a good deed in a naughty world”…… as the Bard saith.
ANDREW
October 25, 2023 at 10:43 pm #17577Carwyn Edwards
SpectatorHi Andrew
Wouldn’t class myself as an expert in electronics and batteries, but I would be wary of anyone selling a AA-sized rechargeable battery with a capacity rated >2850 mAH… as far as I’m aware that’s pretty much the maximum capacity you can currently get in an AA-sized NiCd or NiMH rechargeable battery due to limitations with the chemistry and the size.
You can get lithium-based disposable batteries (not the same as rechargeable lithium ion batteries) which have a rated capacity of 3500mAH for AAs, but these are expensive compared to normal disposable alkaline batteries, but they apparently keep their charge in the cold and they don’t self-discharge in the same way as other batteries so maybe good for a spare torch in the bottom of a pack?
Some manufacturers recommend against using certain types of batteries in their lights too, I have a Petzl Actik CORE, which Petzl say can use alkaline, lithium or Ni-MH batteries (or a petzl-specific rechargeable battery pack), whereas Alpkit apparently recommend against using Lithium disposables in their torches (according to this thread on UKC anyway: https://www.ukclimbing.com/forums/gear/rechargeable_batteries_and_headtorches-486163)
There are a lot of sellers on eBay/Amazon and other online marketplaces that will advertise impossibly high mAh ratings for all sorts of rechargeable batteries, so i’d probably stick to a name brand (e.g duracell) to try and ensure you’re getting the actual named capacity. Panasonic make some batteries under the ‘Enerloop’ brand name which get a lot of good reviews, apparently they work better in the cold than other equivalent rechargables and don’t lose their charge as quickly in storage (apparently), they are pretty extortionate tho (£18 for 4 AA on amazon at the moment).
Modern LED torches will likely all have some internal electronics to maximise efficiency and make the light level consistent throughout the battery life of the light (as well as providing different light levels, flashing modes etc). Battery voltage tends to drop as they get used up and LEDs tend to like having a consistent voltage to work correctly.
In your example of a torch powered by 1 AA battery, there’ll be some electronics there to ‘boost’ the voltage up from the battery-supplied ~1.5V (which in practice for a alkaline battery, could be from ~1.6V to ~1.0V, depending how much juice is left) to what the LED needs, which from memory is around 3.6Vish for a white LED. This boosting process isn’t that efficient, which means some of the battery capacity is going to be ‘wasted’ in the process, which makes a direct comparison hard. I’d reckon the burn time on a single AA head torch is likely to be less than 1/3 of a comparable 3-AA light tho, for the same light output due to those losses.
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