Installing Second Battery In Boat

There are plenty of reasons for you to install a second battery on your boat. As a family of aquaholics, we obviously like to spend time on the water and often find ourselves been one if not the last ones to get out of the water.

I upgraded the sound system on my boat and added more speakers, subwoofer, and amplifier. I knew I needed to add another battery before I drained my boat’s single battery out, playing music all day.

I definitely did not want to be the last one on the sand bar with a dead battery. So I did some research about installing a second house battery and want to share with you what I learned.

Does Your Boat Need A Second Battery?

My answer to this question will definitely be yes, but the real answer is it depends on what you do with your boat and how much do you trust a single battery.

Most people use power regularly throughout the day while boating. Electronics like a fish finder, Chartplotter, radar and VHF radio are usually on all the time. Some people like me even have the radio on playing music all-day

There is nothing wrong with this, the problem is at the end of the day. If your boat is equipped with only a single battery and it is entirely dead, now you are stranded on the water. If you are lucky, someone will give you a jump.

If, like me, you are the last one on the water, you might have to call a towboat, and those can be expensive. It is wise to add a second battery for reliability and added peace of mind.

Types Of Batteries

Lead-acid– is the most common type of batteries for boats. Electrons (voltage) is the effect of the chemical reaction between lead, lead dioxide, and sulfuric acid that happens inside the battery. Here is a quick explanation of how they work so you can decide which one is best for you.

Flooded Battery- Also known as wet cell battery. This is the most common and the mont inexpensive battery out there. It is called a flooded battery because it is filled with liquid sulfuric acid, literally flooding the lead and lead dioxide plates. It is not sealed, and fluid levels must be checked and topped periodically with distilled water to ensure the longest possible lifespan. They are not very good with vibrations, the plates can detach disabling the battery. They are not sealed and must be mounted upright and secured to avoid spills.

Gel Battery- Also known as a gel cell battery. These batteries, instead of having the sulfuric acid in a liquid form, have it on a gel form. The construction of the battery internally is very similar, with the lead and lead dioxide plates. Because the sulfuric acid is on a nonmobile gel form, they dont have to be kept upright, and there is no spill risk. The batteries are sealed and maintenance-free. They are a little more pricey than the wet cell batteries.

AGM Battery– Absorbed glass mat batteries are the newest on the market and are becoming very popular among us boaters. As opposed to the wet cell and gel cell batteries, the AGM batteries have sulfuric acid in fiberglass mats between the lead and lead dioxide. This battery is completely sealed and maintenance-free. They are very resistant to vibration and can be mounted in any position even upside down.

Deep Cycle vs. Starting Power vs. Dual Purpose Batteries

Deep Cycle Battery– These types of batteries are designed to store large amounts of energy and have the capability of being deeply discharged and recharged constantly. The design of these batteries allows them to deliver power steadily for prolonged periods of time with no interruptions. Theis batteries are constructed with thicker plates and a denser active material ratio. You can expect greater run times, better cycling capacity, and a much higher lifespan because of their construction.
Starting Power Battery– Also known as cranking batteries, this type of batteries are designed to deliver a big burst of power for a short period of time enough to start your boat’s engine. Once the engine is running, they get recharged by the alternator. As opposed to the deep cycle, these batteries are not designed to be deeply discharged; doing so will dissolve its plates quicker and shorten its lifespan.
Dual Purpose Battery- Tise batteries combine both technologies providing your boat with the cranking power it needs as well as being able to deliver steady power for long periods of time. They are ideal for small boats with not much room for multiple batteries.

Choosing Battery Cables

Make sure to get marine grade cables for your second battery installation. To ensure proper operation for many years is recommended to use tinned plated stranded copper. Every single strand is tin-plated, this will better resist corrosion and will carry current more efficient with minimal resistance.

Cables come in different sizes. The bigger the cable, the more current it can carry. Consult the engine manufacturers manual to determine the proper size of cable needed for your boat. Not all boat engines and requirements are the same.

The wire size is determined by the amount of amps that it needs to carry and the distance from the battery to the engine.

Make sure to use proper connectors on the cable ends and always use heat shrink to protect the cable from elements. This will help keep water out and fight corrosion on the cable.

Battery Switch

You need a battery switch to have control of how you use and charge your batteries. Battery switches usually have four settings.

#1- This position commonly assigned to the cranking battery. Set the switch on the #1 position to start your engine and keep battery charging while the engine is running.
#2- This position is usually assigned to the house battery, which is generally a deep cycle. Set the switch to the #2 position when anchored on the sand bar listening to music. Position #2 will also recharge your house battery while the engine is running
ALL- Will use both of your batteries together, frequently used to combine resources if cranking battery is running low. Keep in mind that you can drain both batteries if you keep the switch on the ALL position while anchored.
OFF- Set the switch to the OFF position when charging batteries with offshore power. The OFF position will turn everything off on your boat, it is essential to wire bilge pump directly to the battery to avoid accidentally turning it off.

There are other options on the market that manage the using and charging of your batteries automatically. Although a little bit more pricey, these systems take the responsibility of remembering the correct position of the switch and possibly draining both of your batteries.