I know how to calculate current flow across a resister from the voltage, but what about current flow into a battery? Do I need to put a resister in the system so that I know how much current is flowing, or does that drop the voltage to the battery too much? I'm guessing the battery has an effective resistance to it, and as long as the voltage going to it is within specs, the current will be safe as well, and decrease as the battery fills. I'm guessing no resister is needed, and would actually reduce the current flow well below that predicted by the voltage and resistor alone. But I just want to make sure.