DC 5 Volts - 2100mAh Electric Motor Generator. How?
A battery that has an "energy" capacity expressed as 2100mAh is able to supply 2.1mA for 1000 hours or 21mA for 100 hours or 210mA for 10 hours. Or any mA-hour ratio you want providing the hours and the milliamps, when multiplied together equal 2100.

This is not the charging current for said battery because current is measured in milli amps and not milliampere hours.

Now that hopefully you know what you are looking for you might be able to find it and you must ask yourself the question - what current should I be using to charge an iPad - I don't know the answer but you certainly need to find this out. It wouldn't surprise me if it needs a regulated constant current feed. Hey, it might be OK with a plain ordinary 5V feed.