rate = (last measured charge level * 3600 - current charge level * 3600) / elapsed time between the two measurements in seconds

If charge level measurement has unit mAh, then the result will be in mA.

Or in your case with minutes: rate = 4*60 / 10 = 24mA, which sounds like standby current draw when there's some low background internet traffic going on over wifi or 2g.