I got PowerEx 700 mAh 1.2V AAA batteries from http://www.thomasdistributing.com I also got PowerEx 1800 mAh 1.2V AA batteries. I also got a nice MAHA charger that has two independent banks, each of which can charge two AA or two AAA batteries at a time, with a built in battery conditioner and trickle charge circuits. It handles both NiCD and NiMH. The website is a bit chaotic, but they shipped fast, and have little 'free gifts' with the orders, like little battery holding cases and stuff. The PowerEx batteries have great ratings, and are considered some of the best NiMH batteries out there. If the panasonic is designed to charge NiMH batteries internally, then it should charge any NiMH just fine.
Someone said that the proprietary batteries are a bit different somehow, but that they used a bit of scotch tape to 'fix' a regular nimh battery so it would work. I don't know any details, since I don't own any panasonic stuff (I use my AAAs for my total airhead)
sorry if this message is confusing, i've been enjoying some wine.