Boat batteries typically come in two ways: cranking batteries and house batteries. These types don't describe specific battery types but rather their usage on your boat. A cranking (or starter) battery works like your car's battery to get your boat's gasoline engine running. On the other hand, your house batteries (typically deep cycle batteries) power your boat's constant electrical load.

This multi-battery configuration makes sense for larger craft, but what about small fishing boats or bass boats? If you run a smaller vessel, you might be looking to save both weight and space wherever possible. Fortunately, running two batteries isn't your only option, and you may have some room to customize your boat to fit your specific needs.

Why Would You Want Two Batteries? 

Most boat engines, including outboard engines, utilize a starter motor that's relatively similar to those found in automobiles. This starter motor requires a quick jump to get your boat's engine moving, and your cranking battery provides the necessary jolt. Cranking batteries use an internal design that makes them ideal for providing quick power but less-than-ideal for long, deep discharges.

On the other hand, deep-cycle batteries can survive much deeper discharge cycles. If you need to pull power from your battery for a long time, deep-cycle batteries are the ideal choice. As a result, these batteries work better for your boat's "house" load. For large craft, this can include numerous interior electrical fixtures, but for smaller boats, it typically comprises GPS, fish finders, and so on.

There's no question that running two, three, or more batteries makes sense in many large boats, but what about smaller craft? If you're running a small fishing boat, bass boat, or even a fishing kayak, you'll have more options for battery configurations. In these cases, you may be able to save some space and weight by running a single dual-purpose battery.

When Should You Use a Single Battery?

Dual-purpose batteries can function as both cranking batteries and house batteries. However, they typically don't work as well for either role as dedicated batteries of the appropriate type. Instead, dual-purpose batteries are ideal for small, single-engine boats with relatively light running (house) electrical loads. 

Note that there are still situations where a dual-purpose battery may not work. If possible, you will want to calculate the total electrical load of equipment on your boat and confirm that a dual-purpose battery can supply adequate power. Likewise, you'll need to verify that any battery you select will provide sufficient marine cranking amps (MCA) to get your engine moving.

Finally, you may need multiple batteries if you operate with a trolling motor for long periods. These motors draw a lot of power, and they usually work best with one or more deep-cycle batteries to provide extended running times. Be sure to consider all of these factors when designing the battery system that will work best for your specific application.