When a battery does not hold a charge it's most often because the battery is old and lost it's ability to take a charge and hold a charge.
As a battery continues to cycle, it gets thicker.
Eventually, it prevents interaction between ions and the composite materials of the electrode so batteries lose their charge.
Also the batteries water level could be down which is not allowing it to take a charge so make sure the battery has enough water in it.
Things that can drain a car battery when it's off are things such as interior lights, door lights, or even bad relays.
While your engine runs, the alternator recharges the battery — which is why you typically don't have to worry about the battery dying while you're blasting the radio on your drive to work!
If the car battery is not charging while driving then the alternator could be bad.
Car batteries are good for around 3 to 5 years and if your car battery is 5 years old or older it's best to replace it before it leaves you stranded.
If you can turn the engine on, but it dies shortly thereafter, your car alternator likely isn't able to charge the battery.
On the other hand, if you jump start the car and later on it fails to start on its own, it's likely a dead battery.
A corroded or defective alternator diode will faultily continue charging the circuit even when the car off.
This, in turn, will drain your car battery and cause the car not to start.
It is possible to recharge a dead battery, and depending upon the situation you are in, a dead battery is generally an easy fix, whether you are stuck in your garage and can handle it yourself or you are in the middle of nowhere and need professional, quick, and efficient service in the blink of an eye.
Most car batteries that are in good condition will last at least two weeks without needing you to start the car and drive to recharge it.
But if you don't intend to drive your car for some time for whatever reason, you should still start it up once a week to recharge the 12-volt battery.