Don't forget you can buy smart chargers that can in some cases restore a battery that won't hold its charge. Also if your planing on not using your car bike or even boat you can attach a trickle charger to keep the battery in top form. Prevention is better then a cure. I have a charger that will check and restore a battery, monitor and charge a battery over long periods of time while its not in use. And it will also jump start should you be caught out with a flat battery.