5,240 on my 1 year battery 1DMKIII :)

I recently posted about poor battery performance on my 1DMKIII.

I had been getting over 2,000 SPC routinely, when suddenly this dropped to under 600.

Possible causes:
Camera has developed a fault.
Charger not actually charging.
IS on new lens over active.

I'm left with the [Unconfirmed] conclusion that it's the IS on my 'new' 24~105L that was the prime culprit. I did a maintenance charge, even thought this had been done in the last month or so, I stopped using IS and stopped using the 24~105 on my 1DMKIII.

Two charges since showed 4,200 21% remaining and my most recent has 5,240 with 18% and I've recharged at this point.

No indication that a camera or battery charge fault exists ~ can't test the IS ~ but I've seen much reduced performance with extensive IS use before, so that's my conclusion.

I knew IS was going to sap some batt life away but not that much

Do you see this on different batteries? I have seen a few Li batteries on my camera simply drop dramically in their useful charge as they die. As far as I know there is nothing you can do about it or predict it. I have a 24-105 and have not seen a change in the number of images I get per charge on a BP-511 but then again I don't usually get to the point where the bettery is out of charge...

My 24-105 doesn't degrade the battery that much, must've been the maintenance charge, perhaps the one you did last month wasn't enough or something?

I have used a 70-200 with IS active all day and still gotten 4-5000 shots from a battery charge

The way that batteries are treated can significantly affect their ability to accept and hold a charge. Things like running a battery down too far before recharging, overcharging, and storing batteries in a depleted charge condition can all shorten the life of a battery. Additionally, batteries just wear out with use and the more that they are used, the sooner they will wear out. But, on the other hand, not using a battery will also shorten its useful life.Finally, batteries do not have a precise life expectancy and one battery might last five times as long as another.