Deep Cycle Battery Explained for Marine Use
Deep cycle batteries are specifically designed to allow for the gradual depletion of their full capacity over an extended period. For sealed lead-acid (SLA) batteries, deep discharge typically refers to discharging at a 10-hour or 20-hour discharge rate. For lithium iron phosphate (LiFePO4) batteries, the cells are better suited for deep cycle applications. With these basics about deep cycle batteries covered, let’s focus on deep cycle lithium marine batteries.
Types of Marine Batteries
Marine batteries fall into two primary types: starting batteries and deep cycle batteries. Starting batteries, as the name suggests, start the boat’s engine. Deep cycle batteries, on the other hand, can be further divided into two categories: house batteries, which power devices like radios, fish finders, and cabin lights; and trolling motor batteries, which are specifically designed to power your trolling motor. It is common practice to maintain a separate bank of deep cycle batteries in addition to the starting battery to improve battery life and performance. This article will focus on deep cycle marine batteries.
Deep Cycle Marine Battery Sizes
Marine batteries come in various BCI (Battery Council International) group sizes corresponding to the battery’s physical dimensions. The most common sizes include 24, 27, and 31. Generally, a larger case size indicates a larger capacity for traditional sealed lead-acid batteries. This is because there is more room for electrolyte and lead plates, resulting in a higher capacity.
However, for lithium batteries, due to the higher energy density of their cells, the construction of the battery, and a more compact design, batteries of various sizes with different amp-hour (AH) capacities can be produced. For example, the PSL-SC-121000 model battery offered by Keheng is available in both Group 31 (PSL-SC-121000-G31) and Group 27 (PSL-SC-121000-G27) sizes.
These batteries are typically 12 volts (V) and can be connected in series to achieve higher voltages, for example, 36V (three in series) or 48V (four in series). Typical amp-hour (AH) ratings range from 70AH to 125AH, but depending on the size of your boat and its power consumption, you may find ratings as low as 20AH.
Choosing the Right Deep Cycle Battery Size for Your Boat
Before selecting a battery, it is crucial to understand your boat’s power needs, including the duration and frequency of use and the size of the battery compartment. Power-consuming devices on a boat include trolling motors, lights, radios/stereos, water pumps, and household appliances like fish finders. Anglers often use a separate battery bank for the trolling motor than for other onboard appliances.
For example, if a trolling motor draws 25 amps and runs for 4 hours, you will need a 100 amp-hour (Ah) battery. Depending on the voltage requirements of the trolling motor, you may need two or three 12V batteries connected in series to meet the necessary voltage.
In addition to the trolling motor, if you have other accessories that require battery power, such as cabin lights or a stereo, factor the current draw of these accessories into the house battery bank’s capacity calculation.
Estimating Amp-Hour and Voltage Requirements for Marine Systems
Advantages of Keheng Lithium Deep Cycle Marine Batteries
While your marine vehicle may be equipped with Sealed Lead Acid (SLA) batteries, upgrading to Keheng LiFePO4 batteries would be wise. These lithium batteries offer a longer lifespan and are significantly lighter than SLA batteries.
Keheng batteries outperform SLA batteries in both runtime and cycle life. A typical SLA battery can usually withstand 300-500 cycles before reaching the end of its usable life. In contrast, Keheng lithium batteries can achieve up to 4000 cycles, providing 4 to 6 times the lifespan of SLA batteries. Furthermore, lithium batteries provide consistent power throughout their lifespan, unlike SLA batteries, which gradually lose power and shorten cycle length.
Consider a trolling motor powered by SLA batteries. On windy days, a spot-lock trolling motor may gradually lose power. Worse, the spot-lock function may fail to hold position over time, potentially draining the battery completely.
In marine applications, weight reduction is crucial for minimizing drag in the water. For example, if you have three 12V 100AH SLA batteries on your boat for a trolling motor, they weigh approximately 60 pounds each, totaling 180 pounds. The equivalent Keheng lithium batteries weigh less than 30 pounds each, totaling less than 90 pounds—less than half the weight of SLA batteries. This is a significant weight reduction.
How is a Direct Replacement Achieved?
This seamless replacement is possible because Keheng lithium batteries closely match SLA batteries in dimensions and voltage.
Keheng lithium batteries consist of cells and circuits that can accommodate different amp-hour ranges in various size casings. Cylindrical cells are smaller in volume and lower in amp-hours, allowing for flexible series and parallel configurations. Prismatic cells, on the other hand, offer a larger form factor and higher amp-hours, requiring fewer cells to form a battery pack. However, Keheng lithium battery packs are typically smaller than equivalent SLA batteries, allowing for battery packs to be housed in smaller or larger casings. As a result, Keheng lithium batteries can perfectly replace SLA batteries with full-size compatibility.
Additionally, Keheng lithium batteries and SLA batteries have similar voltages. Each Lithium Iron Phosphate (LiFePO4) cell is 3.2 volts. To create a battery pack comparable to a 12V SLA battery, four lithium cells are connected in series, resulting in 12.8V.
This 12.8V is very close to a 12V SLA battery, allowing for easy charging of lithium batteries using SLA charging systems. A 12V SLA battery has a bulk charging voltage range of 14.4-14.7V, while a 12.8V Keheng lithium battery has a charging voltage of 14.6V. Therefore, the lithium battery’s charging voltage falls within the SLA range, ensuring safe charging with an SLA charger.
In conclusion, Keheng lithium deep cycle marine batteries are an ideal replacement for SLA batteries on your boat. This lightweight lithium battery can perform effectively, whether it’s a trolling motor or cabin lighting.