Answer to Question 2.

2. How is the output power rating of the charger calculated?

The output power rating of an industrial battery charger is based on the size of the connected batteries in amp-hours (AH) plus any standing (permanent) load current drawn by connected devices.

A battery can deliver a specified amount of current for a given period of time within a voltage band. In theory a 100AH 12V battery will deliver 10 amps for 10 hours or 100 amps for 1 hour at a voltage of 13.6 down to 10.5 volts DC. It can be safely recharged at 10% of its nominal capacity so a 10-amp charger with a 12-volt nominal output voltage is required.