Question for all of the collective wisdom here:
The other day, I let my sister borrow my 7d. She's used to my dad's 60D, and probably getting a rebel of her own, so I wasn't too concerned about her messing anything up. When she gave it back to me, it wasn't AFing- with any lens, regular or live view, nothing. When I MFd in one-shot mode, I got a focus recognition beep. Checked all the connectors, they were all clean. Finally, I looked at a pin diagram, and seeing that a pin provides 6v for the lens AF motor (something I logically knew, that was just the inspiration) I popped in a fresh battery. Suddenly, AF worked again!
Has anyone ever observed behavior, where a battery shows 2 bars of remaining charge on the top LCD, and the camera takes shots, but doesn't have power to AF?
The battery I had in was OEM. I swapped in a Wasabi power LP-E6 clone- any OEM/3rd party compatibility issues? I'm inclined to think no, since the OEM was the one that caused the problem.
Should I do anything? At this point, this is purely an exercise in intellectual curiosity- that wasabi power LP-E6 has now taken 1,000 shots without issue, so I'm curious more than concerned.
Q1: Nope. Never.
Q2: I have 3 OEMs and one non-OEM. I have let go of the non-OEM because it did not hold charge. AF was not an issue with it. Even the last shot before the camera died would AF.
Q3: So a bit of basic electrical engineering. If that particular battery is not able to deliver 6V to AF when it shows 2 bars, it could be that the battery is faulty. It may be that the internal resistance of the battery is high. It would still generate a voltage that would be considered ok (2 bars), but when it has to deliver the current to the USM to AF, the internal resistance would drop the voltage and hence unable to AF. Then again, this is my best guess (intellectually best guess). Well, I know your question was should you do anything? The answer to that one is a resounding yes
If it is under any sort of warranty, take it back. Internal resistance of a battery is not a function of its charge. It is easily measured. Canon should be able to tell you if your battery is good or not. If it is not, you can leave it with them to recycle it.
Here are some questions I have:
So did you ask your sis if she found that the camera did not AF before she returned it?
Are the battery terminals dirty?
How many pictures can you shoot till this battery goes to 2 bars? And how many can you shoot till the others go to 2 bars? I don't want you to up your shutter count just to answer this question
. Oh! I am assuming the other batteries keep AFing even when they get to 1 bar. If not, we need to have a whole different discussion...
Hope this helps.