Not sure what camera you have, but some cameras require a very steady power supply voltage. Also not sure how old your rechargeable batteries are either, but batteries (alkaline and rechargeable decay over time. With the rechargeable ones, the more you use it, the less it can charge to full capacity over time. For example, if your rechargeable battery is supposed to charge up to 1.5V, over a period of a year with constant recharges, you can test with a volt meter and see that it never really goes back up to 1.5V, but more like 1.48V, 1.45V or maybe even 1.4V.
Depending on the camera or other item you use rechargeable batteries on, it can adapt to low voltages with special circuitry inside (but only to a certain limit, when a battery is old, it is old).
You can try buying a new set of rechargeable batteries and use it few times and see if this fixes the issue. If not, your camera may be faulty and just draining the battery (not too likely, but it happens).
Check out this site for some useful info.