Depends on your audio system and your alternators ability to keep a battery charged per your listening habbits. If the sytem can pull more than your alternator puts out you have to watch your battery.Batteries do not charge themselves and your alt has to have the ability to recharge it under the conditions you use it. Leave a battery sag well bellow a 90% charge (say 70% range) you are killing it much faster than you otherwise would.