I wonder how the new firmware affects this when using 3rd party batteries? From reports I've read elsewhere the battery always reports 100% when using non Canon batteries regardless of the actual charge level. Sounds like 3rd party batteries could be the way forward!
After I applied the latest April firmware update, the 5D3 now behaves just like the 6D. (Canon Battery Nazi - "No battery info for YOU!") In other words, it chastises you when you power on the camera about the battery not being Genuine OEM and then doesn't report any info about the battery except that it's there. So I guess we will have to wait a little while for all the 3rd Party battery makers to hack their battery firmwares to fool the newer cameras. Ugh.