I've had been using the Costco Kirkland AAs for a long time, but I stopped last year due to a perceived shelf life issue.

In an attempt to reduce waste, I use a "battery rotation" in my house. They start in the kids toys. When they reach the "flake out" point (this is where the toy starts behaving like it's demon possessed, saying only one or two words of a song, playing it's "music" without anyone touching it, etc), they get tossed into a "drained" box where they are used in IR remote controls or LED flashlights (I have 15 LED flashlights, story in another thread). When the LED flashlights burn through them, I put them in my IR remotes. They last, literally, for months before the IR remotes kill them. Then they get recycled.

The problem I found with the Kirkland over the Energizer and Duracell (and I'll admit my sample size was two of their 48 packs) was that as I got to about the middle of the 48 pack, the unused remaining batteries wouldn't run the toys. They'd light the LED flashlights about as well as the batteries in the drained box. As this happened twice, my guess was that the Kirkland batteries don't have the shelf-life of the Energizers. I don't think it was environmental conditions--all batteries were stored in the same place and went through four seasons. Two 48 packs of Kirkland and I'm on my third 36 pack of Energizers, though I never hooked it up to a device to get an accurate measurement, so take it for what it's worth.

After getting frustrated with the Kirkland's I decided to bite the bullet and go to rechargable. I went with AA and AAA NiMh batteries. My kids have a lot of electronic toys, and they get rotated into and out of use as they get bored with them. I switched to all NiMh (expensive) batteries, last year (not sure if they had the "fix" that was mentioned about the Sanyo batteries but considering how quickly they stopped taking any charge after very few recharges, I'm guessing not). After the kids used the first set of toys (about 16 batteries worth), I stored them for about 2 weeks as usual (turned off, not removed, I know, I know). When I put them back in rotation, they were completely dead (I didn't measure, but I did put two in my Sony TV remote and no dice). This made the batteries worthless. Kids toys made in the last ten years require tools to replace the batteries and my battery charger only holds 4 batteries, so this is an all day ordeal of charging, watching, changing, charging and of course, figuring out how to get past the child-proof battery holder, putting the batteries in wrong or discovering the need to clean the terminals, unscrewing and screwing them back in.

I did find that if the batteries were fully charged prior to storage, they worked after rotation, but it seemed they didn't work very long.

I'd like to be a whole lot less wasteful (both money, time and materials). Does anyone have any experience with a specific brand of rechargable AA and AAA battery that retains most of its current charge when stored for up to 3 weeks not fully charged (I'll even go through the trouble of removing them from the toys if I have no choice), and from a cost perspective make sense for toys that require batteries to have a discharge rate similar to good Alkaline batteries?

Edit: Clarify storage conditions.