Dropped 20-70 , now battery on 5D3 drained overnight

OOps, 24-70 mark 1.

After the lens dropped, I tried it and all looked ok - focussing as usual. The next day , I found the battery was flat - I then assumed I had got batteries mixed up and put a discharged one back. I charged it again, but found it flat again today. Is it possible the AF is on constantly due to the knock, and thus draining the battery. (I left the camera switched on as usual)

I see by your profile that you have a 5DIII and a 7DII. Is the behavior the same with both bodies? That obviously would confirm the lens.

Or just put the body cap on and see what happens.

Or set the lens to manual focus.

John from PA wrote in post #18469608
I see by your profile that you have a 5DIII and a 7DII. Is the behavior the same with both bodies? That obviously would confirm the lens.

And then try a "Healthy" lens on both bodies as well.
The old human test as they say.

Yep. Try the various suggestions above as well as using a different battery since your post reads like you just recharged the same one and used it again. While the proximity of both events may seem to be related, they may not be. Coincidences do happen.

The 24-70v1 doesn't have IS so no chance the IS motor stuck on, but you might give it a listen and see if the af motor or aperture motor is staying engaged. I'm not sure what sound it would make but something more than silent would indicate one of the motors is not turning off. The only other thing would be a short but I would think that if that had happened, the lens wouldn't work. So many things. Start with the suggestions above and localize the issue first.

gjl711 wrote in post #18471143
The 24-70v1 doesn't have IS so no chance the IS motor stuck on, but you might give it a listen and see if the af motor or aperture motor is staying engaged. I'm not sure what sound it would make but something more than silent would indicate one of the motors is not turning off. The only other thing would be a short but I would think that if that had happened, the lens wouldn't work. So many things. Start with the suggestions above and localize the issue first.

I have a feeling that there would not be the sound of anything actually operating. More likely, something was physically jammed in a "powered" position so the circuit is open but nothing is actually in motion.