Batteries Naturally Discharge – When not in operation, automobile batteries naturally discharge.
Modern cars have upwards of 30 body control modules (computers), warning devices, immobilizers and lock monitoring. All these devices consume power from the batteries. That’s why the battery can be discharged in a week or two for little or no vehicle usage. Vehicles have a small but continuous battery drain.
If it is not kept powered, battery life is reduced – a 12V battery that is not well handled beyond 12.4V will suffer from sulphation. The key cause of battery loss is sulphation. That’s why when cars are left standing for long stretches, the auto battery quickly goes to death.