A "smart charger" should not be confused with a "smart battery". A?smart battery?is generally defined as one containing some sort of electronic device or "chip" that can communicate with a?smart charger?about battery characteristics and condition. A smart battery generally requires a smart charger it can communicate with (see?Smart Battery Data). A smart charger is defined as a charger that can respond to the condition of a battery, and modify its charging actions accordingly.

Some smart chargers are designed to charge:

"smart" batteries.
"dumb" batteries, which lack any internal electronic circuitry.
The output current of a smart charger depends upon the battery's state. An intelligent charger may monitor the battery's voltage, temperature or time under charge to determine the optimum charge current and to terminate charging.

For?Ni-Cd?and?NiMH?batteries, the voltage across the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage?decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, "delta-V," or sometimes "delta peak", charger, indicating that they monitor the voltage change.

The problem is, the magnitude of "delta-V" can become very small or even non-existent if (very) high?capacity rechargeable batteries are recharged.?This can cause even an intelligent battery charger to not sense that the batteries are actually already fully charged, and continue charging. Overcharging of the batteries will result in some cases. However, many so called intelligent chargers employ a combination of cut off systems, which should prevent overcharging in the vast majority of cases.

A typical intelligent charger fast-charges a battery up to about 85% of its maximum capacity in less than an hour, then switches to trickle charging, which takes several hours to top off the battery to its full capacity.