A CRV3 battery (also know as CR-V3) is used in various electronic appliances, including many digital cameras. The CRV3 is the shape and size of two side-by-side AA batteries to equal a nominal voltage of 3V. This allows CR-V3 batteries to be used in many cameras and other devices originally designed only for AA batteries.
An RCR-V3 battery is a rechargeable 3.7 V lithium-ion battery, that can be used in place of a CRV3 battery. Because both Lithium and Lithium-ion chemistries offer higher energy density than alkaline or NiMH batteries, a CRV3 battery will typically last much longer than a pair of AA batteries.