Many things can cause a car battery to lose its charge. Battery problems are considered minor problems, but the causes behind a battery losing charge can prove expensive. Inspecting your car can go a long way toward finding the real reason your car battery won't stay charged.
Car batteries lose their charge for several common reasons; a jump may be needed only for certain reasons. Leaving your headlights or interior lights on, leaving the radio on when the car isn't running, or a faulty mechanism that leaves the trunk light on once it's closed can cause your battery to go dead. If the trunk light is the problem, take your car for service to get the issue repaired or it will continue to drain your battery.
Take a look at the battery before you try to test it. Sometimes the cables that connect the battery to the car can corrode and not let the battery hold the charge properly. If the cables look fine, continue to follow this method. It will help determine whether the battery is dead or if the stalling is due to another problem. Make sure the engine is turned off, and turn on the windshield wipers or headlights. If the wipers move extremely slow or the headlights are abnormally dim, this means the battery is probably discharged. If your battery is relatively new, you'll need a jump. If the battery is a few years old, you'll probably need to replace it.
Take a look at your exposed belts. Belts such as your AC belt, serpentine belt and other associated belts can usually be seen without looking too hard once opening the bonnet. Apply pressure to each belt to check for any looseness. The belt should stay in place when pressure is applied. Look for wear and rotting in the belt material. A belt wears over time and can dry out like a rubber band, which may cause it to stop working correctly or even snap. Loose belts just need to be tightened.
Alternators are responsible for charging your battery, and can lose power for many reasons. Have your alternator tested before replacing it to ensure that's the problem. Alternators are tested by testing the "diode trio," which is a converter of the alternating current (AC) to the direct current (DC). The equipment tests to see whether one of the diodes has failed, causing the alternator to fail or not generate enough current. This and voltage overload can cause an alternator to fail.
If you don't have the money for a battery or to replace your alternator, there are a couple of things you can do. You can carry some jumping cables in your trunk so you can jump-start your battery if it continues to die, or invest in a Self Charge Auto Jumper like the one made by Wagan Tech. These devices charge your car without the presence of another car to charge your battery, and they plug into your cigarette lighter outlet. This costs half the price of the battery.