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How to Charge a Boat Battery With a Car: Step by Step Guide

How to charge a boat battery with a car
How to charge a boat battery with a car


The technology of batteries and chargers always keeps up with incredible advances in modern designs for cars and boats. Different purposes are served by each of these modern boat batteries and each has been designed with various advantages where disadvantages may occasionally follow. At one point, regardless of the battery type being deep cycle or cranking, they must be recharged. Here, we discuss step by step guide how to charge a boat battery with a Car or Vehicle.

Another significant aspect of marine batteries, regardless of the variety- AGM, flooded, gel, or even Lithium-ion is that their response to charging may be different. Using the proper and right battery charger preserves the lifespan of your boat’s batteries.

Some people take boat batteries for granted, just as they would for car batteries, and let them sit all winter, thinking an occasional charging blast will keep the battery healthy. Unfortunately, the result may lighten your wallet with a need for new battery purchase about every other year.

To further the point, depending on the storage method and environment, a battery can lose up to 30% of its charge per month just sitting around. This is one of the factors that most people do not consider. Environmental factors can be a state of discharge, battery age, temperature, humidity, etc.

How to Charge a Boat Battery With a Car – The Basics of Boat Batteries

Cranking and Starting Batteries

Modern boats are more advanced, with sophisticated sensors, pumps, and computers for a newer model outboard. For this reason, these boats must get enough starting power. These battery types are projected particularly to start the boat’s main engine.

The internal usage of thinner and more numerous solid lead plates ensures more surface area, allowing the hefty amounts of energy quickly that tough starting jobs require.

The alternator easily and quickly replenishes the used energy inside when the motor is active. You can always figure out the amps in the owner’s manual. So, for the recommended Marine Cranking Amps (MCA), check the book. MCA measures a battery’s number of amps to be delivered at 0°F for half a minute without dropping below from 7.2 volts rating.

Deep-Cycle Batteries

Such battery types are technologically advanced to power onboard electrical accessories. A deep cycle is a concept of using slow-rated energy without having to be recharged until the day ends.

So, they can be dependably used in advances like GPS, trolling motors, radios, or fish-finders. Deep-cycle batteries provide more strenuous discharge while withstanding the sternness of hundreds of discharge/recharge cycles, which cranking batteries fail to achieve. This deeper battery type requires a different design type of thicker and fewer lead plates to defy the deep cycling.

How to Charge a Boat Battery With a Car – The Guide

While charging a deep cycle battery from your car is possible, one warning must be added. The deep cycle battery you aim to charge must be 12-volt. Batteries like a 6-volt golf cart cannot be charged this way without damaging both vehicles. Attaching the starting battery and the deep cycle in parallel connection will charge them.

Nonetheless, discharging these battery types by over 50%, it has the probability of shortening the battery lifespan drastically. During the power breakdown, having the deep cycle battery type is wired to the car the whole time necessitates a battery isolator. It prevents the car from starting while ensuring the starting battery is not discharged.

The requirement for a battery isolator comes because the alternator of a car or a boat is not very dissimilar. Both have voltage regulators to ensure a slow charge for the battery to near a full charge and simultaneously prevent boiling all batteries.

But remember, the need for an isolator comes only if the deep cycle battery is supposed to stay connected the whole time. But for a simple charging process, unhooking the battery should suffice.

Another addendum must be added where the engine speed should be brought up to around 1500 rpm. It will turn the alternator movement into turning faster, rendering a higher charging rate. At 500–700 rpm, the alternator has an idle speed, so it cannot produce moderate charging capacity.

Swapping out the batteries will make the fully charged car battery be overcharged. In contrast, the other battery primarily intended to be fed will take longer in the process since the same charge rate will be sent to both batteries by the alternator.

The charge rates hugely depend on the alternator, but the battery charge level and the alternator load also decide.

Technically, a deep-cycle battery is processed with thicker plates. Now, Start by checking connections for loose ones because they can make the batteries seem dead even though they have a full charge. The marine battery should stand in parallel against the car battery.

The car battery must not go through any disconnection made when fully charged itself. The alternator of the idling engine will control the marine battery’s charging procedure. Nonetheless, 12-volt batteries hook simply up to an alternator.

However, for 6-volt batteries, they need to be cabled in series. The first battery’s negative (minus) pole must connect with the second battery’s positive (plus) pole for a voltage additive of 12 volts.

For the connectivity of the charger, have the plus pole of the first battery and the negative pole of the second battery screwed in. You have to sit back for hours until the boat battery finally has charged.

How to Charge a Boat Battery With a Car – Conclusion

While following through with the charging process, maintenance is also required. The charge rate and full charge voltage are generally available over the battery body and online for the marine battery. Cautionary steps include cordoning the area off to vulnerable animals and children and being alert of stealing.