I just thought I'd share some of my findings with the forum since I don't often see this sort of info passed around and it's something that we all have an interest in.

So. The ubiquitous "AA" cell (not a battery; a battery is a group of cells). We toss them in our flashlights and radios and remotes and everything else. But there's a couple different types available now. What do they all mean?

1.) Alkaline cells. These are the most common sort on the shelves today and every major manufacturer has a line it seems. Alkaline cells have a nominal voltage of 1.5V, but their output voltage drops as the battery is depleted. Most devices that use this type of cell will stop working when the voltage gets to the 1V-0.8V range, at which point the cell still has some unused energy in it. Digital devices, which only work at a very small range of voltages, will stop even sooner. Alkaline cells have less capacity the harder you push them: while an AA might have a capacity of 3000mAh (millamp hours) while driving a load of 50mA, the same cell might only deliver 1500mAh when driving a load of 300mA. Alkaline cells will retain most of their charge for years, and you can usually count on a pack of AA's that's been sitting around for a while to still be useful.

2.) Zinc chloride cells. So called "heavy duty" or "super heavy duty". Again, very common. They are only "heavy duty" in comparison to the carbon-zinc chemistry they replaced many decades ago. These are usually much cheaper than alkaline. These cells have less than half the capacity of an alkaline. They will last 2 or 3 years on the shelf, at which point the active ingredients inside will begin to literally dissolve the casing. These cells suffer from the same voltage depression problems as alkaline, and most devices will cease to function long before the cell is actually depleted. They are noticeably lighter than alkalines. While not good for long term storage or hard use given their lower capacity, the very low cost of these cells makes them attractive for "buy it now, use it now".

3.) Lithium. These are not lithium-ion rechargeables, they are one-use and disposable. Lithium AA cells are made to have a voltage of 1.5V and are interchangeable with alkaline/zinc AAs, while the basic lithium chemistry (commonly used in "button batteries" and CR123 camera batteries) is 3.6V and are not. They are not as common as alkaline, and cost several times more. Lithium cells deliver a very constant voltage until they are nearly depleted, meaning that devices, especially digital devices, while continue to run for nearly the cell's entire capacity and are not strongly affected by the degree of load on them. They don't hold any more energy, they are just more efficient at delivering it especially under high loads. Lithium cells have an extremely long storage life (10 years or more), which makes them attractive for disaster kits. They also work at low temperatures, while other chemistries deliver less and less power as they get cold. Finally, lithium cells are noticeably lighter than alkaline.

4.) NIMH. Rechargeables. These hold less energy than an alkaline AA (typically 2000-2500mAh to the alkaline's 3000+), but like lithium cells they deliver a very consistent voltage until nearly empty so you can extract everything they've got. These are expensive compared to disposables, but will probably last between 500 and 1000 charges at decreasing amounts of capacity until they become useless. NIMH cells have a voltage of 1.2V, but because devices that run on alkaline cells are designed to tolerate their falling voltage as they become depleted, they are interchangeable. The so-called "memory effect" is not applicable to NIMH cells, and in fact draining them completely before each charge will wear them out faster. NIMH cells work better than Alkalines at low temperatures, but they still are not happy about it. Regular NIMHs will lose 40% of the charge per month, or more, so you should be sure to charge them before each use and are useless after storage. Recently introduced are "low discharge" NIMH cells (much less common, and more expensive), which will still hold 80-85% of their charge after a year's time and start to be practical for storage.

A side note on NIMH Cs and Ds: read the package. The big name battery manufacturers do not make a true C or D rechargeable. What they do is take an AA cell and put it in a different canister, which keeps the cost low. However if you read the fine print, the "C" and "D" cells will have a capacity of only 2000 to 2500mAh. A true C-sized NIMH should have a capacity of around 6000mAh, and a true D-size should have around 10000mAh. Currently these cells are only sold by lesser known companies like Accupower.

Yes, good post. Thank you.

Good info. That is why I mostly use alkaline except in my devices that are stored. For those I use the the lithium which has the longer shelf life as you stated. Can alawys depend on you for good solid info. Thank You. <img src="/ubbthreads/images/graemlins/thumbup.gif" alt="" />

i have several packs of eneloops. two of them are the duracell repackaged eneloops, marked "made in japan." the "made in china" marked rechargable duracells are not eneloops, but i have a pair of those and they work fine too.

i don't use alkalines anymore, except the 9v in my guitar pedals.

OK- I'll bite " What are eneloops" ? <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

Eneloop is the new version of NiMH battery. It is suppose to have lower self discharge rate compare to the lower kind.

Right, those are the low discharge types. I'm pretty sure "Eneloop" is a brand name, not an accepted technical type, so I didn't mention them specifically. :| There are several eastern groups that sell that type of thing under different names.

(frankly I'm of the "call it what it is" school, so "low-self-discharge NIMH" is my pick)

You mentioned it briefly, but when the cold weather camping season hits, I switch over to lithiums for the cold weather performance. I am not much into babying stuff, and trying to keep stuff warm all the time.

In headlamps and such in freezing temps, lithiums are the way to go.

All other times, I just go with alkalines.

I found it interesting that Petzl, one of the more popular headlamp manufactures, specifically states not to use lithiums in their headlamps due to overheating problems. Supposedly they can produce higher voltage than alkalines during their life cycle, even though they are all specified at the same voltage. Don't know for sure. I am also guessing that if you used them strictly in freezing temps, overheating may not be an issue? Not sure....

Engergizer on the other hand claims to replace any device damaged by their lithiums.....so go figure. I would still hate to be in the field and have a light fail, even if it could be replaced for free.

I just decided not to worry about it, and use Princeton Tec headlamps. They have no issue with the use of lithiums. Can you tell I like camping in the cold??? <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />

B

There are also Nickel-Cadmium rechargeable or NiCAD cells.

Although the only place I see these anymore are Radioshack, these cells are similar to Alkaline cells in the fact that they lose power steadily until depleted, whereas Lithium and NiMH maintain steady power until depleted.