Let preface by saying, I am a proponent of using genuine camera batteries where possible. I believe they usually have better quality control, generally offer the best capacity and will tend to last better in the long run. However the cost of the genuine Panasonic GM5 is fairly exorbitant where I am (~$90AUD each). So I decided to pick up some generic batteries instead. I didn't want to get the cheapest and nastiest batteries from ebay, so I got some from this store: http://www.betterbatt.com.au/s/digital-camera-battery/panasonic/dmw-blh7e/BBCB-361/. They don't seem to over-rate their battery capacity and claim to provide some sort of support behind their products. Whether these are truly better than the cheap batteries from ebay, I do not know. The Panasonic battery is rated for 680mah. The generic is rated for 600mah Anyway here is the initial discharge capacity test of these batteries. Tested at a 300ma discharge. Betterbatt Generic A - 561mah Betterbatt Generic B - 579mah Genuine Panasonic battery - 660mah. So the Generics and Panasonic batteries are relatively close to their rated capacity. The Panasonic battery has more capacity than the Generics. Personally I feel generics tend to fail/lose their capacity quicker over time. So it would be interesting to do these test again in 12 months time, to see where we are at.