A deep cycle battery is one that can be discharged repeatedly of a high percentage of its capacity, and a deep cycle battery charger is a device that connects to this type of battery's terminals and feeds it electrical energy so that it can recharge. There are many types of chargers, and they draw their power from a variety of sources. A deep cycle battery charger is usually connected to a charge controller. The charge controller might be external, like it is when solar panels are used as a battery charger, or it might be incorporated into the charger, like it is with a portable deep cycle battery charger.
Deep cycle batteries are used to provide power for, among other things, marine engines, living spaces for boats and recreational vehicles and the electrical needs of solar houses and other houses that use alternative energy sources. When they are used in a boat or vehicle, they are usually connected to a deep cycle battery charger that draws power from the vehicle engine. In an alternative energy home, the alternative energy generator is the charger. It can be a wind turbine or an array of solar panels. In addition, it is possible to plug a portable deep cycle battery charger into a household electrical outlet and use it to charge a battery.
The process of recharging a battery has three distinct stages. In the bulk stage, the battery is fed a large current and its voltage steadily increases. The absorption stage begins as the battery nears it capacity, and at that point, the input current should steadily decrease until it is fully charged. In the float stage, a small constant voltage is maintained across the battery terminals to keep it fully charged. The function of the charge controller is to monitor the battery charge and regulate the incoming current so that the battery does not overheat or overcharge.
A charge controller is an essential component of a deep cycle battery charger. It not only protects the battery, it also prolongs its life by charging it safely and keeping it charged. Vehicles and handheld plug-in devices often incorporate a smart battery charger with a built-in charge controller. Other chargers, such as solar panels, are usually wired to an external controller, which is then connected to the battery terminals. In a solar energy system, the controller performs a dual function, protecting the battery bank from overcharging while also protecting the solar panels from a back-feed of power from the bank, which could damage the solar cells.