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I decided to buy rechargeable batteries and wow, is there a lot of information on them! I found this site was recommended: http://www.thomas-distributing.com/index.htm

Does anyone have any other advice? I plan to use AAs which are for my lights. I'm not sure what brands are good, and what are not. Thanks!

Briefly:

All other things being equal, lower capacity cells may endure more cycles.

For cells likely to be left in a torch for some time after charging (many weeks to months) it's worth considering Eneloops or similar Low Self Discharge cells, since although their maximum capacity is low (~2000mAh), they hold a charge much better over time, and seem to have good endurance in terms of number of charge cycles

There are some notable lemons out there. (Energiser 2500's seem to have a bad reputation).

A good source for finding people praising and complaining about rechargeable cells is: http://www.candlepowerforums.com/vb/for ... ay.php?f=9

potholer wrote:There are some notable lemons out there. (Energiser 2500's seem to have a bad reputation).

Not to pick a fight but there is also some notable misinformation out there. Personally, my Energizer 2500 NiMH sets have been going strong for about a year (but I'll keep my fingers crossed just in case). I use these in lights and digital cameras/slaves, and I recharge a set every week or two on average. I charge them on a ~1-hour charger.

You could think about checking out the new hybrid NiHMs too. They are supposed to really hold their charge, giving them a good shelf life. Apparently they lose as little as 20% of their charge over a whole year! If you get them from one of those stores that have a 90 day return policy, you can always take them back if they don't live up to your expectations anyway...

The Energiser 2500 issue does seem to crop up on candlepowerforums with at least enough regularity for me to remember it, though it may well be there were just some bad batches, and complaints may be amplified by the same people making comments multiple times. Still, given a choice of cells, I'd probably weigh 2 or 3 failure stories about the same make/model of cell as balancing out quite a few success stories.

There do seem to be general patterns - especially at the cheaper end, across brands, highest capacity cells (2500/2700) seem more prone to failure or fast self-discharge than lower capacity (~2000 or less), but there are definitely exceptions as well, with some brands being particularly good at all capacities.

*Personally* speaking, having used cheap-brand cells bundled with various chargers, the 2300s (various brands) I've had have been the least-long-lasting, whereas older 1800/2000/2100s, even sometimes from the same brands, lasted much longer even under the exact same usage regimes.

Typically, I'll use batteries in my headlamp for trips over a weekend averaging about about 24 hrs and then not use them again for a few months. Does that change things?

If you're always going to be charging up shortly before use, the low-self-discharge cells do lose their main advantage, and if your trips aren't too frequent, then the number of cycles that cells can sustain is maybe not too important either, as long as you don't get actively poor ones.
Getting decent capacity cells from a good-reputation manufacturer may be the best bet (Sony do seem to get pretty good comments), but I guess it depends what's available in your neighbourhood.

As a general rule, whatever brand of cells you use, if you're using multiple sets of cells on a trip, it's generally going to be best to swap to a new set before the current ones are entirely flat, since out of a set of cells, often one or more flatten before the rest. Running the light after some cells are dead flat can seriously shorten those cells' life.
If you have more than one set of cells that look the same, it's worth marking sets of cells to avoid the possibility of getting them mixed up at different states of charge. Depending on the pack sizes sold, and how many cells you need to make up a set for your lights, it may even be an idea to deliberately buy different cells to make sets more identifiable.

Gracias! I'm off to check out some of the links above now.

Remembering this old topic, I felt a quick follow-up was appropriate.

It would seem potholer's earlier comments were correct. Now, after about 2 years of use, my 20-or-so Energizer 2300 and 2500 mAh NiMHs seem to be dying off pretty quick - even with no load (kept in a bag). Yet my bunch of 4-5 year old Rayovac 1800s, while admittedly not used much in the last couple of years since I had the Energizers, are still going strong. My current preference for NiMHs are the new Rayovac Hybrid 2100 mAh. They cost about $9 for 4 AAs or 4 AAAs. I think I got my first set about 9 months ago, and so far so good.

Still beats using Alkalines all the time, though.

I'm definitely a convert to Eneloops.
Though I don't use them in my main light (it takes homemade packs with larger cells), they sit in my rarely-used backup Minimag (LED), and get a brief topping-up every few months, and I use them for almost all my other AA requirements.

I have begun buying eneloops, but am also a big fan of the Maha Powerexbrand batteries sold by Thomas Distributing.

If I need the highest possible capacity and can recharge them soon before a trip, I go with the Maha Powerex 2700 mAH batteries.

For electronics that I want to work a few months from now and may sit for significant times between use, the Eneloops are my top choice, even though they sacrifice some capacity for their low-self-discharge properties. Also, the Eneloops are claimed to be better at delivering power under heavy load better than standard NiMH, but I am not smart enough to understand exactly why this is even though I have read such claims at Candlepowerforums. Eneloops are hard to find, but the Duracell "Pre-Charged" NiMH batteries sold at Walmart that are made in Japan and have white tops are actually re-branded Eneloops. The Made in China Duracells are claimed to be inferior over at CPF.

I can also say from personal experience that the Energizer 2500mAH batteries are crap. I've experienced rapid self-discharge, much lower than advertised capacity, and batteries that have stopped accepting a charge. YMMV

Heat is the enemy of rechargeable batteries. Fast charging generates a lot of heat quickly, which isn't good for battery lifetime.

Sometimes, people will confuse a certain type of battery or high-capacity battery with poor performance/life when it is really related to the charger (say, 1-hour charging).

All batteries will benefit from lower charge rates to a point. I use a 4-hour charger, and my 2.25 AH AA cells have been working for 4+ years now with no problem in digital cameras, GPS units, and headlamps...

Just another opinion...

karst97 wrote:Heat is the enemy of rechargeable batteries. Fast charging generates a lot of heat quickly, which isn't good for battery lifetime.

Yeah, I agree. A friend loaned me his fast charger (15 minute type) once, and that permanently fried a couple of sets of my batteries really quick!

I have a couple of slow overnight chargers which take maybe 8 hours to charge, but I mostly use another charger which takes about 1.5-2 hours and then switches to trickle charging. Batteries normally get a little warm during charging, but I've recently noticed my dying 2500 mAh NiMHs get quite hot. A good reason to replace those ones, I think.

I like the look of some of the newer (more expensive) chargers where you can set the charge current/time and each cell is individually monitored/switched during charging. Maybe my next charger will be one of these.

Yes, heat buildup during charging is bad for your batteries, but you should never use a cheap charger that operates on a timer (15 minutes, 1 hour, 4 hour, etc). My suspicion about the Energizer crap 2500 cells is that the batteries might be ok but the cheap timer charger is responsible for cooking the batteries.

Instead, use a "smart" charger that is able to measure voltage and determine when the batteries are no longer accepting any more charge and all the energy is being converted to heat.

The best one out there is probably the Maha C-9000 charger sold by Thomas Distributing. Sure it seems expensive, but having your batteries perfectly charged and being able to measure their actual capacity is incredibly useful. You don't want to have one bad cell ruin your day because you didn't know it had crapped out, especially when underground.

Even the small charger that comes with Eneloop batteries is a smart charger.

If in doubt, go to candlepowerforums and ask the folks there if your charger is a smart or stupid one.

karst97 wrote:Heat is the enemy of rechargeable batteries. Fast charging generates a lot of heat quickly, which isn't good for battery lifetime.

Sometimes, people will confuse a certain type of battery or high-capacity battery with poor performance/life when it is really related to the charger (say, 1-hour charging).

All batteries will benefit from lower charge rates to a point. I use a 4-hour charger, and my 2.25 AH AA cells have been working for 4+ years now with no problem in digital cameras, GPS units, and headlamps...

Just another opinion...

From what I've read, for NiMH cells, if a charger really is smart, and does proper termination, there are some advantages to relatively fast charging (1-2hrs) in terms of what happens to the cell internals. It's also a bit easier to reliably terminate charging at 1-2hr charge rates.

However, there are a lot of poor cheap allegedly-smart chargers out there, and a good slower charger is much better than a poor faster one.

I think there's definitely a charger component to cell failure - coupling a poor charger with the less-good varieties of high capacity cells is going to be the fastest way to end up with dead cells.

I'd echo the praise for the Maha charger - not cheap (and not compact) but certainly useful.

I started using the Energizer 2500 batteries for work a few years back. Several of them failed after less than two years. Last year I bought a MAHA C-800S charger and and reconditioned the "failed" batteries. They work great now. I mix batteries a lot. All Energizers but the ratings are 1850, 2100 and the 2500. With this charger I don't worry about it as it charges each battery independently. I never use the rapid charge mode. It's just habit as I place the first battery in the charger to hit the soft mode button. My trips are seldom more than five hours but there are times I'll use them five days a week at work then maybe another short trip on my days off. Mostly if I'll be on a longer trip I'll use carbide so I don't know that I'll ever know how long they can last.