I stock a bit of everything, but the core is lithium AA and lithium 123A cells. I also keep some lithium AAA and lithium 9V cells. I buy all online and in bulk to save cost.
On top of that layer, I keep alkaline cells. I limit this to a couple of bricks per size and pay attention to the expiration date. I keep mostly AA and AAA alkalines, but also some D cells and C cells, even though I don't really have much use for them.
I also keep a smallish rotation of high capacity NiMh AA and AAA batteries. I've found that less is more with these. You get too many and you won't be able to keep them charged. Another key here is to get a smart,
independant channel charger.
Sanyo 2700 mAh Industrial Grade AA NiMHMaha MH-C401FS 4x Independant channel AA/AAA smart chargerI've really pushed my gear towards 123A and AA. I should say I've pushed it towards 123A, but you can't avoid AA.
The key IMO is to get multi-output LED lights. Combine these two features and you will get a LOT more milage from your battery stockpile.
The WORST are the incandescet 2D flashlights. D cells are particularly problematic as their discharge curve is pitiful. Combine this with an incandescent bulb, and you get a light that gets dim and yellow quick. In the end, it weights a lot, takes up a lot of space, and you get lousy runtime. Worst of all worlds.
So if I *know* I'm going to use my light for a long time, I'll put some of the NiMH cells in it. If the light is getting stored, lithiums go in it. If I'm going to lend it to someone, I'll probably put alkalines in it. If you have an application where you go through batteries a lot, but rechargables don't make sense for one reason or another: alkalines.
Another good option if you can pull it off is a light that takes rechargable lithium ion batteries. My EDC is a
HDS EDC Ultimate 85 with a 2x123A battery pack, and outfitted with a lithium ion 17670 battery (same size as 2x123A). I carry some 123A spares.
I have a couple of the lithium ion batteries that I rotate so when I want to swap, I always have a fresh cell to drop in. The beauty of this light is that it was designed to take these lithium ion rechargable (lower voltage than 2x123a).
The downside is there are not that many lights that are designed to take these cells.
Since I got my U85 and lithium-ion cells, my usage of 123A cells has dropped almost to zero. :-)
-john
Note the NiMh rechargables, like the lithium cells are good for high drain applications like digital cameras. Much better than alkaline.
The lithiums have a slightly high starting voltage. This is normally not a problem in most applications, but beware of applications using several in series since the small difference adds up. So, if you have a 4AA or greater application, make sure the mfg says lithiums are OK.
The NiMh are lower voltage than alkalines, but the voltage doesn't sage as much as alkalines. So, your alkalines might be brighter initially, but soon they will drop off and the NiMh cells will keep going strong.
Also beware not to over discharge your rechargable cells. This will kill them, or lower their lifespan.