I replaced the 7 month old batteries in my superflash over the weekend. They were still running fine just a bit dimmer than they should be. I replaced the alkaline batteries with NIMH rechargeables (800 MAH) that should have been fully charged. I ran them for about 3 hours on flash over the past 2 days. I went to turn them on this morning and got a big nothing.

The whole thing seems odd to me. I get 7 months out of a dollar store battery and 3 days out of rechargeables? Anyone else have problems?

Rechargeables can do that.

I use 1000mah duracells and get about 15-20 hours of runtime before they need to be recharged..

depends on the rechargeables, a high capacity one will have a higher self discharge and will be more affected by cold temperatures. a low self discharge like an eneloop may last longer.

Those problems are not typical, so I suspect at least one of your cells is weak.

could be energizer 2500's then it would be typical, I still see those ripoff's in the stores.
post the brand/model of battery.

I prefer the Lithium AAAs in my PBSFs in the winter...neither alkalines nor NIMH rechargeable seem to do well in temps below freezing.

I have 2 sets one energizer and one Sanyo. The ones I was using at the time were energizer....

Sounds like it might be time to get a new charger. Or it is time to go the P7 route....

If they are in fact energizer 2500's those are know to be just about the worst batteries there are. Combine that with the 15 minute "charger" (more liek a cooker" that comes with them, they usually don't live past 50 cycles.
If your going to rely on rechargeables then get a decent charger and decent batteries. A charger that charges based on current not time if what you want to look for.

The hi-discharge cells (>2000mA) are notoriously bad compared to regular batteries for low-discharge charge sustenance. I have Eneloops (2000mA) and while they hold their charge a lot better than standard NiMHs, for me, they still lose about half their charge in about 6 weeks in lo-drain equipment such as Superflashes, pagers, and clocks. Still, I use NiMH rechargeables for my PB Superflash - I really like to keep 'em hot.

For a charger I have this thing. It is reasonable charger but lacks the fanciness of some of the newer ones.

The system was working fine for me until I got a AA powered bike light. Now the rate of use is requiring a bit more management...

Try searching at candle power forums for that charger to see if its decent or not. NiMH really shouldn't be tricle charged wtha mantenance charge, it tends to reduce life. My bet is a bad cell, knoing you have the energizer 2500's makes it even more likely. You need a charger that can test them to find out. I have the maha c9000 for example, just popped a set in last night and ren the refresh/analyze and cecked this morning to see if they were all good. I'll do that every 10 to 20 cycles to check them.

I've had great luck with Enoloops in lights, and horrible luck with Energizers.

I'm using Sanyo Eneloop AAAs in my PBSFs and not having any problem. You have something defective.

I use Maha chargers and a ZTS tester. After several weeks of use they seem to ZTS test at about 60%.

Energizer has some known bad models, like the 2500's which die an early death after just a few uses. At one time they were sending coupons for replacements but they were only good for other energizers so most poeple were just replacing them with alkalines.
Don't let some back companies like them get you down in rechargeables as I did in the past, buy some eneloops and give them a try.
If you had an AA light I'd say go buy some eneloops and if they didn't work I'd buy them from you but I don't have much that needs AAA's

Did you charge them first? You need to do that.