Operator errors, such as leaving a device turned on, and malfunctioning parts, such as a bad alternator, are common reasons for a dead vehicle battery. Replacement parts may be necessary to resolve persistent problems with the battery.
Lights or other devices that are left on for a long period of time may drain the battery. For instance, allowing a mobile phone charger to remain plugged into the lighter port may cause the battery to lose its charge. Turn all devices to the off position, unplug car chargers and check hidden areas, such as the glove compartment, to ensure all lights are off.
A poor connection between the battery terminals and the battery posts can prevent the battery from working properly. Check the battery cables and terminals for signs of corrosion or damage, and make sure the terminals are tightly connected to the posts on the battery. Clean or replace the terminals and cables if needed.
The alternator is responsible for maintaining a charged battery. Test the alternator with a multimeter, or take the vehicle to an auto parts store that offers free testing to determine whether the alternator is working properly. The alternator may have to be replaced if the car starts with a jump start or loses power when the headlights are turned on. If the battery is older than a few years, it should be replaced to ensure there isn't a slow leak in one of the cells.