The term lead-acid battery often conjures up the standard flooded batteries found in automobiles and 80% of all production ships. The three basic types of batteries used in the marine industry are composed of lead and acid: submerged or wet batteries, AGM (absorbed glass mat) batteries, and sealed gel batteries. Lead-acid batteries are further subdivided into three application-based categories: priming, deep cycle, and dual-use.

   Advantages and Disadvantages of Valve Regulated Lead Acid (VRLA) Batteries

    Valve-regulated lead-acid (VRLA) batteries can be installed in any position, except upside-down, due to their sealed, spill-proof design. If you plan to mount the gel battery sideways, expect to lose 10% of the amp-hour (Ah) capacity. When faced with a flooded bilge situation, the VRLA battery will continue to operate at a depth of 30 feet. After the first water depth, this may not be practical.

    The low self-discharge rate of VRLA batteries is much better than that of flooded lead-acid batteries, which makes the shelving time maintenance-free.

    Unlike most automotive-grade flooded lead-acid batteries, AGM batteries won't drop plates or disintegrate when subjected to shock in rough seas or excessive hull vibration. This is because the inner plates on the AGM battery get additional physical support from compressed fiber mats sandwiched between each lead plate.

    The cost of a deep-cycle VRLA battery is about twice the cost of a regular deep-cycle flooded battery or about 20 percent more than an advanced flooded battery. If you decide to upgrade, remember to consider the additional cost of modifying the marine battery charging system to meet the VRLA required charging regime, unless you are installing Spiral Battery AGM batteries that are compatible with most alternators.

     It is not recommended to discharge deep cycle batteries below the 50% depth of discharge, which is half the battery's reserve capacity rating. Every time a deep cycle battery is discharged to 100%, the battery will lose at least one cycle of the battery's total lifetime rating.

    How to test deep cycle VRLA batteries?

Step 1: "Conditioning" the Battery

First, condition each cell at room temperature by discharging each cell to 50% depth of discharge (DOD), then wait six hours for the cells to cool before using Xantrexs new XC5012 Series Triple/50A Digital Charger. Each cell underwent four discharge/charge cycles. Most battery manufacturers state that their products require 10-25 cycles for optimal performance.

Step 2: Test the battery's spare capacity to discharge

    After the batteries were conditioned, fully charged, and rested overnight at room temperature, the first round of reserve capacity discharge testing began. During discharge, maintain the electrolyte temperature in the range of 75 F - 90 F using any convenient method. Discharge ends when the voltage across the battery terminals drops to the equivalent of 10.5V, noting that the discharge duration is in minutes. When the VRLA battery voltage drops to 1.75V per cell (a 12V battery has six cells x 1.75V per cell = 10.5V), its depth of discharge (DOD) is called 100%.

    The varistor potentiometer adjusts the discharge rate and compensates when the incandescent lamp load draws less current at the end of the test cycle due to the voltage drop. After reducing the voltage of each cell to 10.5V, remove the cells from the test stand and allow them to cool overnight before charging. After six hours of charging and cooling, the 25A load test was performed again. These two numbers were then averaged and recorded as the observed discharge duration.

Changshu Wanlong Power Technology R&D Co., Ltd. is a lead-acid battery manufacturer and storage battery manufacturer from China, Sealed Deep Cycle Battery. The company sells sealed solar batteries, and sealed maintenance-free batteries all year round. The quality reaches the international standard and the performance is outstanding.