Shouldn't matter unless you have a really monster battery charger. An eGo or Riva big battery fast charger only draws 500 mA, which is the minimum spec for a USB port on a PC. Typical KR808D-1, standard 510, other standard battery chargers will only draw somewhere around 100 mA.
For charging, as long as the USB power source meets the input spec on the battery charger piece, any extra mA don't do anything -- the charger won't draw more current than its input spec.
I don't worry too much about computer damage from a battery charger. While undoubtedly possible, I think that failure mode is less likely than a pass-
through short (I always run pass-
throughs off a dedicated power supply, not off my PC).