If you’re wondering, “What type of battery do I need for my boat?” or “Which type of battery is best for powering an electric trolling motor or as an electric boat motor battery?” Learn about boat battery types so that you have a general understanding of the best boat battery to use in different situations.
Types of Boat Batteries
Batteries on boats handle two basic kinds of tasks, which are starting an engine and running electrical loads like lights, electronics or accessories for longer durations of time. Many boats use two different types of batteries -- an engine starting battery and a deep cycle battery for powering navigation, lights, and electronics.
To choose the best boat battery, you’ll want to first determine the battery's application and then choose from the battery chemistry: AGM, wet cell, gel, or lithium. It’s also important to check your boat battery cables for any splits, frays or corrosion when replacing your marine batteries as part of your boating safety routine.
Boat Cranking Batteries
Since starting a boat engine requires a lot of power in short bursts, a boat cranking battery is a lead-acid battery that is made with thinner, more numerous lead plates. The marine cranking amp (MCA) or cranking amp (CA) rating found on a battery's label ranks the battery's starting power. Check your engine manual for the recommended MCA/CA rating before you shop for a battery and choose a battery with a rating equal to or greater than the recommended value.
Deep Cycle Batteries
Electric trolling motors, sonar, and other accessories draw power at a slower rate for extended periods of time. These deep discharges can be hard on battery plates, so a deep cycle battery is the best boat battery type to use. Deep cycle batteries have fewer but thicker lead plates than cranking batteries and are built to withstand deep cycling. A deep-cycle battery's reserve capacity (RC) rating will indicate how long it can carry a specific load before running out of charge. A deep cycle battery also can withstand many discharge/recharge cycles, while a boat cranking battery isn’t made to be completely discharged.
If you own a small boat and there's only room for one battery due to space or weight limitations, consider buying a dual-purpose battery that handles both starting and cycling. Keep in mind though, that most dual-purpose batteries won't start an engine as well as a boat cranking battery and won't handle as many deep discharge and recharge cycles as a dedicated deep-cycle model.
Batteries are further categorized as AGM (absorbed glass mat), wet cell, gel, or lithium depending on the chemistry or conducting medium inside of the battery.
AGM (absorbed glass mat) batteries have porous microfiber glass separators compressed between the battery's positive and negative plates, which are saturated with just enough acid electrolyte to activate the battery. AGM batteries have a long life, low self-discharge rate, and are good dual-purpose batteries for boaters who require fast recharging, quick starting power, and reliable deep-cycle ability.
Wet cell batteries
Wet cell batteries use a reservoir of liquid sulfuric acid, so they produce hydrogen and oxygen when the battery is being charged. Wet cell batteries allow the gases to escape into the atmosphere, unlike gel and AGM batteries, which recombine the gases and re-introduce them to the system. Wet cell battery boxes and compartments must be vented to let the gases escape safely.
Gel batteries are spill proof, submersible and leakproof. A sealed, valve-regulated design nearly eliminates gassing, so they are safer to install around people and sensitive electronics (although gel batteries still need to be vented). This type of battery chemistry needs carefully regulated smart charging to prevent damage.
Lithium batteries weigh less than lead acid batteries, can be discharged 800 times to 100% depth of discharge, and can be recharged in a little over an hour, but a lithium boat battery generally costs quite a bit more than other battery chemistry types.
Once you have your batteries installed, don’t forget to register your boat and take a boater’s safety course.