Intelligent chargers test the battery before starting to charge it to determine it's capacity and state of charge. The charge rate is varied according to the heat generating characteristics of the battery. Some also monitor the battery temperature. A technique known as 'Delta V cutoff' detects the small voltage drop in a battery just as it reaches a full charge. This allows charging to be stopped at the appropriate time. Intelligent chargers dramatically shorten the charging time, provide longer run times, and prolong the working life of a battery.