Um you can... In theory, I guess. I think the charging cord is only supposed to pull the power it can handle from the power source, etc.
However, you would be doing yourself and your mod a big favor if you bought two new
batteries from recommended suppliers (See Mooch's blog, someone will link it) and a decent external charger.
These removable batteries aren't really designed to be charged by USB over the long haul. You can in a pinch but it's probably considerably safer not to.
Anna