What is a smartcharger?

What is a smartcharger?
A basic battery charger is just a current source which runs at a slightly higher voltage than the battery being charged. If a regular charger is left hooked up, it will eventually damage a battery.

A smart charger usually has extra intelligence added in two critical points. The first is that the charger will usually adjust the charging rate (amount of current used) based on the battery's current state. Commonly, this means there are a few charge rates used, with a high rate used for a very discharged battery, a lower rate for most of the charge cycle, and then even less for the last few percent of the charge. The rates may also differ depending on the type of battery detected, as different battery technologies (basically the chemicals used inside and the materials dunked in the chemicals) need charged at different rates. It may also not be a constant rate; sometimes it's useful to charge at a varying frequency (more current, then less, then more) to help "condition" parts of the battery. It's more technical than this, but you hopefully get the ideal

The other level of intelligence is often the ability to charge at a very low rate indefinitely; enough to maintain the battery without overcharging and causing damage. This feature is usually referred to as either maintenance charging or float charging, and is particularly useful on batteries which are stored.