When choosing an onboard battery charger, it is important to choose a device that is compatible with your battery. You have to consider important features such as type, input voltage, amp-hour capacity, and the environment you will be using the battery. The biggest killer of batteries is overcharging. If possible, an internal and intelligent battery charging and maintenance device should be preferred for such batteries. Charging time is a determining factor in this regard, as well. More discharged batteries or smaller alternators require more time for a charge.