In order to choose the best boat battery charger, it is necessary to remember that many boats use two different types of batteries. Another key to properly charging a battery is to use a very slow battery charger to bring it up to a full charge. Charging a battery too fast can often result in a battery that will not hold a charge for a very long time. A trickle-type charger is the proper unit to use on most batteries.
While the cranking or starting battery on a boat is nearly always a 12-volt, high-amperage battery, many boats also are often equipped with a 12-volt, deep-cycling battery as well. This battery typically powers optional equipment such as trolling motors and fish-finding electronics. While both of these batteries are 12-volt, they require different types of chargers to properly maintain them and keep them fully charged. Using the wrong boat battery charger on either one can damage the battery beyond further use
When searching for the best boat battery charger, purchase a unit that includes a quick connect/disconnect fitting which allows the battery to be charged and maintained without removing the battery from the boat. Often, the manufacturers of the top-of-the-line chargers also will have additional quick fittings. These can be added to auxiliary batteries or batteries in other vehicles, enabling the charger to be used on a wide array of vehicles.
When selecting a boat battery charger, choose one which has settings for starting as well as deep-cycle batteries. This eliminates the need for two separate charging units to maintain a single boat. Top-of-the-line models will allow charging and maintenance of both types of batteries at the same time. While this charger within a charger is more expensive initially, when compared to the purchase of two individual high-quality chargers, it is often very reasonable.
If the price of a boat battery charger is not an issue, select one that incorporates an automatic restart in case of a power failure. In the event of a power failure, the typical charger will simply turn itself off, which can lead to a drained and dead battery. With an automatic restart feature, the device will turn itself off and then back on periodically. This not only saves power, but also prevents over-charging if the battery is hooked up to the boat battery charger for prolonged periods of time between uses.