Replacing a car battery on older vehicles used to be simple!! You unhook the old battery and install the new one. Late-model vehicles, however, rely on computers that operate everything from the stereo to the transmission. If power is disconnect from ecu, the settings will lost and have to reset to default. That means the vehicle may feel different when driven, and you may have to enter a security code to access the stereo. Using this simple memory saving device when replacing your car battery will help you avoid these problems.