Join date: Nov 7, 2022


Types of Deep Cycle Boat Batteries

Lead-Acid Deep Cycle Boat Batteries

Lead-acid deep-cycle marine batteries come in two main varieties: flooded lead-acid (FLA) and absorbent glass mat (AGM).

Flooded lead-acid batteries are the most basic type of lead-acid battery. They contain a sulfuric acid solution with lead plates suspended in it. You need to monitor them continually and periodically add water to the batteries to keep them operating correctly.

Absorbent glass mat batteries are also sometimes referred to as sealed lead-acid batteries. As this name implies, the batteries are sealed and don’t require the same maintenance as FLA batteries. AGM batteries also have lead plates in them, but they sit between electrolyte saturated fiberglass sheets.


Lead-acid batteries are the most common and readily available type of deep-cycle battery. Since they are readily available, it’s usually pretty easy to find a replacement if you need one. They also have the lowest upfront cost, which can be enticing to those on a budget.

Lead-acid batteries do not have any electronics in them, which allows them to provide a large amount of current. This makes them a good option for starting batteries.


Lead-acid batteries have a few major drawbacks. The first is that they require more maintenance than other deep-cycle batteries to ensure they remain in peak working condition. While AGM batteries don’t need the same maintenance as FLA batteries, they cost significantly more without adding any additional capacity.

Deep-cycle lead-acid batteries should not be discharged below 50% of their capacity. Doing so will damage them. Additionally, as lead-acid batteries discharge, their voltage also drops. Combining these two factors means that you typically only get about half of the rated capacity out of a lead-acid battery.

While deep-cycle lead-acid batteries have the lowest initial cost, they also have the shortest lifespan, lasting only 2-5 years. Because of the lead plates, lead-acid batteries are very heavy, which is not ideal for boating applications where weight is a vital concern. Lastly, FLA batteries are not sealed, so you must install them upright to prevent the acid solution from leaking.

Lithium-Ion Deep Cycle Boat Battery

Lithium-ion deep-cycle batteries use lithium salt to store energy instead of sulfuric acid and lead plates. They are relatively new and are still the most expensive type of deep-cycle battery. However, their high upfront cost is often justified by their many advantages, especially in boating applications.


You can drain lithium-ion deep-cycle marine batteries to 80% or more of their capacity without damaging them. Additionally, with the proper charge controller, they charge much faster than lead-acid batteries. This combination makes lithium marine batteries much more efficient than their lead-acid counterparts.

Lithium-ion batteries have an integrated battery management system (BMS) that monitors the battery’s health and eliminates the need for periodic maintenance. The BMS also optimizes charging and discharging across the battery’s cells and ensures the battery is always operating within its safe limits. These features result in the lifespan of a lithium battery being 2-5 times that of a lead-acid battery.

Lithium-ion deep-cycle batteries don’t contain heavy lead plates and weigh about half what lead-acid batteries of the same capacity do. As we mentioned earlier, this is a massive advantage in a boat where every pound counts.


The biggest disadvantage of lithium-ion marine batteries is their initial upfront cost. However, you often end up saving money in the long run since they usually last at least five times longer than traditional lead-acid batteries.

One other thing to consider is that the maximum amperage output of lithium-ion batteries is much less than lead-acid batteries. This means that lithium-ion batteries are not a good option for a starting battery where you need high cranking amps.

Tina Yu

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