Funnily enough, I did quite a bit of rummaging on the net about this a few months ago and found all sorts of conflicting info. I tried it on a couple of defunct batteries and it worked with limited succes. From my limited attempts it didn't seem to get the batteries back to their 'pre-knackered' state although there was an improvement. I was probably doing it wrong.
My wifey tried Reiki on my bike with a dead battery, I had to go and hide round the corner as she did her her hands off healing business.
It did not work.