Selecting the correct charger depends primarily on the design of your deep cycle battery, so the first thing you need to do is determine the construction type of your battery. There are a few popular types these days, and each has its own unique characteristics. One charger will not work for all types, so this step is very important. The four most common types of deep cycle batteries are wet cell, gel cell, absorbed glass mat, and the valve regulated lead-acid type, or VRLA.

Most people are familiar with the wet cell battery. Just like an automotive battery, this type has a liquid electrolyte that fills internal compartments, or cells, in which lead plates are hung. This is the most common type of deep cycle battery and is available off-the-shelf at most sporting goods and major department stores. The AGM (absorbed glass mat) construction uses a woven mesh material to absorb the electrolyte and keep it in constant contact with the lead compound. It is a sealed design and considered maintenance free, unlike some of the wet-cell batteries. It is, however, quite similar to the wet-cell and can use the same type of charger. The VRLA is also of sealed construction, but its main differentiation is that is uses an internal valve to vent the gases created during the charging cycle. It also can use the same type of charger as the wet-cell batteries.

A multiple stage deep cycle battery charger is used for the three battery types listed above. This charger comes in many sizes, so you do have to match the correct charger for your size battery. If you have more than one battery installed in your power supply, then you will need a multiple bank type charger. This is actually two, three, or even four chargers built into one unit. Depending on what country you live in, you also need to match the input voltage of the charger to the correct voltage of your service. If price is a major factor in your purchasing decision, you will find many basic deep cycle chargers available off-the-shelf. These will be lower priced, manually operated, and with few special features built in. You will need to start and stop this charger manually in most cases, and unhook the connectors when not in use. You will also need to manually set the dials and switches on the front panel for each operation and different battery that you charge.

If you are maintaining a higher quality battery, you may want to consider purchasing a "smart charger" instead. The smart charger is simply a computer controlled charger that actually takes readings from the battery it is connected to and then sends the proper charging voltages and currents necessary to provide a complete charge. Many of the smart chargers also have a built-in equalizing charge that kicks in after the primary charging is completed. This equalizing process evens out the charges in the individual battery cells.

The fourth type of battery, the gel cell, is considered a deep-deep cycle battery as it is designed to for extended cycle times and consequently, longer recharge times. The electrolyte inside the gel cell battery has been mixed with a thickening agent to solidify the solution. A "smart charger" is the preferred choice for maintaining the gel cell, but primarily because the gel cell is most susceptible to damage from over charging or improper charging. This type of battery can endure higher ambient temperatures that a wet-cell battery and can provide extended operating times that other battery types, but it does require special equipment to maintain it properly.

A good quality charger can take much of the guesswork out of properly maintaining your deep cycle marine battery. Whether you use a low-cost basic charger or a state-of-art smart charger, following a strict battery maintenance routine can ensure many years of trouble-free life from your trolling motor battery and other deep cycle batteries that you use.