Choosing a Battery


Most boaters take their batteries for granted. Actually, choosing the battery is a very important aspect of boating.

First of all, Marine batteries are more expensive due to their construction. Do not pick a cranking battery or deep cycle battery that is intended for use on land simply because they are cheaper. Marine batteries have heavier plates and stronger internal construction. They are built to withstand the pounding the rough seas can deliver or the rough ride fishing can bring on your boat. Choosing the right type of battery is most important.

Cranking or Starting and Deep Cycle

Starting or Cranking batteries yield a lot of power in short duration. They crank the starter of your boat’s engine and are the sprinters of your electrical system.The design provides the electrical push necessary to turn over motors. That push is usually measured in cranking amps. The Marine Cranking Amp (MCA) measures that starting power. Always choose a battery with a rating equal to or greater than the recommended value. Starting batteries have thinner and more numerous plates, providing extra surface area to generate high amperage bursts of current. However, because of this thinner construction, the plates are relatively fragile in high-impact environments. Also, starting batteries do not tolerate deep discharges, which reduce their operating lifespan. They are not designed to be totally discharged.

Deep cycle batteries are built to deliver smaller doses of power over a longer period of time. They power the electrical loads on your boat when no charge source is available. Trolling motors and accessories use power at a slower rate for extended periods. They are designed to be discharged down as much as 80% time after time, and have much thicker plates.This power is measured in Amp-Hours. Reserve Capacity indicates how long it can carry a specific load. The higher the RC number, the longer the battery will power the accessories. A deep-cycle battery will have two or three times the RC of a cranking battery. Also, a deep-cycle battery can withstand several hundred discharge/recharge cycles.

Let’s discuss the 2 most popular types of batteries used in boat applications. Which type you choose is based on your needs, the capacity & lifespan you are looking for and your budget.

GEL batteries are filled with liquid electrolyte that is gelled with silicates before the battery is sealed. It is impossible to spill acid even if they are broken. They use recombinant technology that eliminates the need for adding water. They self-discharge at only three % per month, handle the highest number of lifetime charging cycles, are maintenance free, spill-proof, submersible and leak-proof. They have other advantages. They are low-temperature tolerant, shock/vibration resistant and have long cycle life, however, their most notable advantage is resistance to over-discharge that can damage other battery types. They have an internal self-discharge rate less than 1 percent per month, so they can be stored for long periods without being recharged. It’s easy to forget to recharge batteries promptly after use. Gel Batteries are a good choice because they aren’t prone to develop life-shortening plate sulfation when left uncharged. One disadvantage is that they must be charged at a slower rate (C/20) to prevent excess gas from damaging the cells. They cannot be fast charged on a conventional automotive charger or they may be permanently damaged. They also cost slightly more than other battery types with the same RC and MCA ratings.

AGM (Absorbed Glass Mat) batteries feature fine, highly porous microfiber glass separators compressed tightly between the battery’s positive and negative plates. Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. Nearly all AGM batteries are “recombinant”. What that means is that the Oxygen and Hydrogen recombine inside the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost. AGM’s have a very low self-discharge, from 1% to 3% per month is usual. This means that they can sit in storage for much  longer periods without charging than standard batteries. They are shock and vibration resistant & submersible without damage. AGM batteries also can be installed at any angle. No maintenance is required, except periodic external cleaning.

Batteries come in different sizes. Many have “group” sizes, which is based upon the physical size and terminal placement. Typical BCI codes are group U1, 24, 27, and 31. Industrial batteries are usually designated by a part number or letters  such as “GC” for golf cart or “FS” for floor sweeper. Other standard size codes are 4D & 8D, large industrial batteries, commonly used in solar electric systems. Many batteries follow no particular code, and are just manufacturers part numbers.

No matter what kind of battery chemistry you choose, follow these recommendations to get the best performance:

1. Do not mix old batteries with new ones in the same bank. Old batteries tend to pull down the new ones to their deteriorated level.

2. Stay with one battery chemistry. Each battery type requires specific charging voltages. Mixing different types can result in under or over-charging. This may mean replacing all batteries on board at the same time.

3. Keep batteries clean, cool and dry. Clean corrosion with a paste of baking soda and water.

If you take good care of your batteries, they will last for the specified time suggested by the manufacturer and allow you to enjoy your time in the water without worry..

 East Coast Marine Battery