A battery is an essential part of a car's electrical system. It provides the power necessary to start a vehicle. It also supplies power to such things as the stereo, lights and climate controls when the car is turned off. But car batteries can lose their charge, often without any warning, leaving you stranded. It is important to troubleshoot a battery that won't keep a charge to ensure that this doesn't happen again.
Turn on the headlights to check the output of the charging system and the battery. If the headlights work and are as bright as they normally are, then it is not the battery. It may be a bad starter or connection between the solenoid and the starter. If the headlights come on but are dim, check the battery's voltage.
Check the voltage of the battery with a voltmeter. Select the option for either a 12- or 20-volt scale and connect the red test lead to the battery's positive terminal. Connect the black test lead to the negative terminal. Check the digital reading on the voltmeter--if it is below 12.4 volts, the battery is low and should be recharged.
Recharge the battery by hooking it up to a battery charger. Remove both the positive and negative battery cables and attach the battery charger's positive and negative outputs to the corresponding battery terminals. Allow the battery to charge until the charger indicates that it is fully charged.
Unhook the charger and connect the battery cables to the battery. Start the car and check if the battery will hold a charge by connecting a handheld electronic battery tester to the battery terminals. The tester will indicate if the battery is capable of holding a charge or not. If it is, you have solved the problem. If not, replace the battery.
When removing battery cables, remove the red, or positive, cable first. Connect the black, or negative, cable first when reconnecting.