I've not seen that, and I don't think it would be the expected outcome.
Is this with a grip?
70-300mm vr lens at 300 VR on.
I was panning to shoot a Barn Owl 15 feet away and the lens just refused to focus and all I am left with is 6 frames full of a white blob :bang: I was not a happy bunny.
Has the 70-300 got a focus limiter on it? If so was that inadvertently switched on?
I'm incling to think that the battery level is unrelated and that something else was the cause. How much ambient light was there? Was there enough for the AF system to work?