The drainage topic I've heard of is the fact that, if you leave it charging overnight for example, on the PC, the PC sometimes - not always - throws a tizzy, has a funny turn, goes to sleep, whatever, which changes the charge into a drain.
So I always charge from the mains with a mains charger - doesn't have to be an expensive Sony one by the way, just nothing Apple-y.
And it does give a better charge - don't ask me why, it just does - and a lot quicker.
