A fascinating read from Imaging Resource: The Great Battery Shootout
The Rayovac 1600’s came out on top, but the Powerex 1700 and GP 1800’s come within 0.2% of the Rayovac’s performance and are available much cheaper. I’ve been buying batteries from Thomas Distributing for years and highly recommend them (they also sell the much more expensive battery packs most new prosumer digicams are using).