geradov on twitter let me know about a problem he was having with his batteries on his 5D mk ii. He's narrowed it down to the grip. He's added his description of his situation to this DPReview post where someone else reported the same issue. You should read the whole thing, but here's a summary:
“After doing some tests I noticed that when using the vertical grip, the battery discharges at a rate of 20+% every day, which is obviously not good. In my case I also noticed the BG-E6 vertical grip, when attached to the camera it makes my zoon in / Focus Point select button to fail (in both, the camera and the grip), not sure if that is related to the battery issue but it certainly is concerning.”
Anyone else having trouble keeping batteries charged in the grip? Sound off in the comments please.