I have a weird problem and wonder if anyone has any input. A customer shooting a 40D found his battery drained in about 60 shots when he started shooting with an 85 f1.2. His camera doesn't exhibit the problem with any other lens so the obvious assumption was something about the 85 f1.2 which was exchanged for new 85 f1.2. The new one also drains his 40D in 40-50 shots. He gets hundreds of shots with a 24-105 f4 IS, and the problem has repeated with a different battery.
I remember someone on POTN reporting this problem (Username wimg).
Personally, I shoot this combo (40D/85L) frequently and have not seen anything similar. I've gotten well into the hundreds of photos on a battery charge without dismounting the 85L, though a single session was never over 100 shots.
I had this issue, and posted about it here. I tried the lens with other bodies, no drain. I tried the body with other lenses, no drain. I tried with grip, without. Just to be clear, when I take the battery back into the cam, it will resume to the full capacity, and will drain again in a matter of shots. Cgardner mentioned something about its a safety characteristic for over/under current, or something to that effect.
I sent in the lens, and they changed some circuitry. But still exhibited the drain.
I sent the 40d next, and they changed something there as well. I have no more issues with the pair.