RE: How do chargers work?
A battery charger is a DC power source which is connected to a battery in parallel. (Positive to Positive and Negative to Negative)
A battery charger should only be used with a rechargable battery and with the proper type of battery the charger was designed for.
The charger operates at a voltage slightly higher than the battery voltage. The Higher voltage on the charger pushes current back into the battery in a direction opposite to how it came out. This reversed current flow (Charging Current)causes a reversal of the electro- chemical reaction used in the battery that produced electricity.
The amount of voltage applied to the battery from the charger determines how much charging current flows. Charging current determines how fast the battery recharges.
The speed of recharge effects how much heat is generated during recharge. Too much heat build up(from high charging currents) can damage the battery. (Warp plates, boil off electrolyte, cause pressure build up and rupture the battery)
Recharge rates can also effect longevity of the battery. Trickle charging with low currents is slower but doesn't stress the battery.