It was mostly a tongue-in-cheek remark

. In that you can charge a battery by reversing the current. How long it takes to charge it depends on the current. I have no idea if the ipad has circuitry to set a threshold current for charging or even how much it draws in standby or off. I think you will want a minimum of 1.8 Amps and comfortably 2 Amps for our application.