It can be any number of problems...my security system was draining my battery. Start troubleshooting the problem by pulling out your fuses one-by-one and seeing which circuit is responsible. It will show up on an amp meter connected to the battery when you plug the fuse back in. You could have a hot wire grounding out, a faulty switch, a relay that is stuck or even a demon-possessed alarm system. Two other circuits that generally don't have fuses are the starter and the headlights. You can test them by disconnecting the cables that go to them.
Then, again, it could be something as simple as a bad battery. If you put a fast-charger on the battery you may have fried it. Get it tested before you do anything else.
It might need a new battery.
Dead battery
the alternator is bad
Sulfation can happen when battery is not fully charged and remains discharged
Maybe your alternator needs replacing.
Dead cell in battery or something is on pulling power from the battery. Disconnect the negative battery cable overnight with the battery fully charged (12.6 volts). If the battery is dead the next morning it has a dead cell and needs replacing. If however the battery is still fully charged then a light is on somewhere or a relay is stuck closed.
Then something is on pulling power from the battery. Any light on the vehicle or any relay that is stuck closed.
It could be a number of things. First check that the battery is fully charged.
Dead cell in battery, defective alternator, or something is on pulling power from the battery.
YOU HAVE TO TURN IT ON Actually, I learned this past week that if it is a gel type battery, you can get a false positive on the battery, so it looks like it is fully charged but actually is not. You can take the battery to your dealer to see if he can charge it or you need a new one.
try taking your altenater off and taking it to your nearest autoparts store and they can test it . the altenater is what keeps your battery charged i hope i have helped
Take it to your local auto parts chain store. Most of them will check your battery and alternator for free.