What are lithium deep cycle marine batteries?

What are lithium deep cycle marine batteries?

Deep cycle batteries are designed to continuously and stably provide energy to systems, and they have their entire capacity consumed from the battery very slowly over time. LiFePO4 batteries, also called energy cells are used for deep cycling purposes. Let's go to learn more about deep-cycle lithium marine batteries.

Marine Batteries

There are two types of marine batteries, starting batteries and deep-cycle batteries. As the name suggests, starter batteries are designed to start the boat's engine. Deep cycle batteries can be further split into two groups - On the one hand, deep cycle batteries can power the electronics of the boat, such as the radio, the fish finder, and house lights. On the other hand, deep-cycle batteries can be used to power trolling motor. To optimize batteries' life and their performance, it is often common to have a separate deep-cycle battery pack in addition to starting batteries.

Deep Cycle Marine Battery Sizes

Marine batteries typically come in a series of group sizes that are equated to the physical size of batteries. The most common sizes are 24, 27, and 31. when we look at traditional sealed lead acid batteries, they are usually assumed that the larger the case size is, the more capacity they have. This is because the bigger case provides more space for the lead plate and electrolyte, which means higher capacity.

The Enjoybot batteries are offered in 12-volt, 24-volt, 36-volt, and 48-volt. Users can order a single of these sizes and also can connect battery packs in series to bring the total voltage up to 24V (2 12V in series), 36V (3 12V in series), or 48V (4 12V in series). The most common amp-hours (AH) is between 100ah and 400ah. People can choose the right size depending on the size of the boat and the power draw.

How to Size a Deep Cycle Battery for your Boat

Before picking batteries for your boat, you will have to understand the power requirements, how long and how often you will use it, as well as the size of the battery cabinet. Items that might be pulling power on your boat include: trolling motor and a household power source, such as lights, radio/ stereo, pumps, and fish finders, among others. often times, fishermen will use a separate battery pack for their trolling motor instead of using them on other electronics on the boat.

For example, if your boat has a trolling motor that would use 25 amperes and be in use for 4 hours, you will need a 100-ah (amp-hour) battery to run the trolling motor for that long. Depending on the trolling motor's requirement, you will require a 24V to 36V battery, meaning you may need a single 24V to 36V battery, or two to three 12V batteries pack in series to meet the requirement.

If you have additional accessories requiring battery power like house lights, a stereo, or a fish finder, you would also need to take those amperage requirements into account of how large to size your additional accessories' battery bank.

A great formula to use would be: Estimated run time (hours) x estimated amperage needed = total amp-hours required.

Once you have the total amp hours required, you need to check the voltage requirements of your system. It is crucial to match the system's voltage with the voltage of your battery packs. For example, trolling motors typically require 12, 24, or 36 volts of batteries. Thus, you may need two to three batteries connected in series to match the voltage requirements for your trolling motor. Additionally, to your convenience, you can also pick a single battery of 12V, 24V, and 36V  to set up on your boat.

Benefits of Lithium Deep Cycle Marine Batteries

While most people may use SLA batteries in their marine, however, with the advancement of technology, LiFePO4 batteries are considered a great highlight in the replacement and upgrading of SLA marine batteries. This is because LiFePO4 batteries are designed to last longer and weigh less than comparable SLA batteries.

Lithium batteries are more durable than SLA batteries in terms of operating time and cycle life. The SLA battery only has 300-500 cycles before it has ended its life. The average lithium battery will have 3000-5000 cycles before it has reached the end of its life. This is about ten times longer than the SLA battery. Besides, lithium batteries almost can provide consistent power delivery across each cycle for the entire lifespan. Whereas SLA batteries will gradually begin to deliver less energy and shorter cycle lengths as time goes on.

Let's assume a trolling motor using an SLA battery. If it is a windy day, the spot lock of the trolling motor will gradually lose power. Even worse, the spot lock function of the trolling motor may stop holding its lock as the day goes on, and the batteries may even die. With a LiFePO4 battery pack, even on windy days, the battery can continue to operate without ever losing energy and also never losing the spot lock.

In marine applications, it is an idea to lighten the load as much as possible to reduce resistance in the water if you have three 12V100AH SLA batteries on the boat for the trolling motor. For instance, they would weigh approximately 60 pounds each, a total of 180 pounds. The same size of lithium batteries would weigh less than 30 pounds each, and less than 90 pounds total - less than half of the SLA batteries. This is a significant weight savings.

How is the drop-in replacement possible?

It is possible as the lithium batteries' form factor and voltage are very closely matched to the SLAs', making for an easy drop-in replacement between chemistries.

Lithium batteries are composed of cells and circuits, which can fit varying amp-hour ranges in different sizes. Cylindrical cells are a smaller form factor, and they usually featured lower amp-hours, however, they can allow for many units in series and parallel. Prismatic cells are larger form factors, they featured much higher amp-hours. This means that users can connect very limited battery packs in series and parallel. In most instances, a lithium pack is smaller than the SLA equivalent battery. Thus, users can use a smaller case or a larger case to encapsulate the pack. This allows for lithium to be a physically fit drop-in replacement for SLA.

Likewise, lithium batteries and SLA batteries are similar in voltage. Each lithium iron phosphate (LiFePO4) cell is 3.2 volts. To make a battery pack that is close to a 12v SLA battery, lithium batteries connected 4 cells in series to make 12.8V.

Although the lithium of 12.8V is close enough to the voltage of a 12V SLA battery, and the bulk charging voltages of a 12V SLA battery are 14.4-14.7V, the charging voltage of a 12.8V lithium battery is 14.6V. However, the SLA charging system is unable to charge lithium batteries. Because they are composed of different chemistries, and their working principles are different. If misuse their chargers, it will cause damage or shorten their lifespan.


Marine lithium deep cycle batteries are an excellent alternative to SLA batteries. From trolling motors to house lights, the lightweight SLA alternatives can provide power for all functions.

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