As a general rule, electric vehicles are designed to be charged overnight. Depending on the charging system, you may need to leave it plugged in all night to get a full charge. Most electric cars have a monitoring system that maintains a trickle charge as the battery approaches full, to ensure that it does not exceed the maximum. While plugging it in for 8 to 12 hours is expected, you should consult the car manual if you plan to leave it plugged in longer. Electric cars need to be used regularly, with charging in-between to maintain the battery.