I've gone to Energizer 2450mAh rechargeables. I have the Energizer 15-minute fast charger that does four of them in short order. The problem I'm having is that they seem to charge down very quickly. I recently replaced the analog thermostat in my BOQ with a digital one. It requires two AA batteries to maintain the programmed settings. The batteries discharge to the point that the low-battery reminder comes on in less than 24 hours. This seems strange because I can take about 400 pictures with my digital camera using rechargeables, as opposed to about 100 using alkalines. I leave the batteries in the charger until the cooling fan has turned off, so I know they are getting a full charge. Any ideas?

Self discharge rate ? This is proportional to amp hour rating .That's why the special low SDR batteries I have are 2000Ah rather than anything higher.SDR is also a matter of purity .The purer the components the lower the SDR.

That's charged shelf life.
Rechargeables have less voltage 1.2 to start. Then lose a lot quickly, put em in a transistor radio, loud when fresh, then a fast drop.
Try lithium batteries, they are expensive but last ages.