Rechargeable batteries perform a little differently than non-rechargeable batteries. The voltage coming from an Alkaline (non-rechargeable) battery decreases steadily as the battery is discharged. Ni-MH and Li-Ion batteries have a lower starting voltage than Alkaline (typically 1.2-1.3V vs. 1.5V for Alkaline), but rechargeables maintain this level until they are almost discharged. One potential problem: the battery life indicator of the camera may be calibrated for alkaline batteries, which could make it somewhat inaccurate.