Extend the life of your batteries

Be good to your batteries

Next to the grating sound of your prop trying to chew a channel in a hard bottom, nothing is quite as sobering as the silence following an attempt to start your engine when the battery is dead.

Just like your oil level, engine temperature and draft, your batteries require regular attention whether they’re flooded, gel or absorbed glass mat lead acid batteries. Let’s look at the different types.


Flooded batteries

Flooded batteries have caps that can be removed to add distilled water. Never add tap water to flooded batteries, because the dissolved minerals can cause the individual cells to discharge when the engine is off.

Although the least expensive type of marine battery, flooded batteries require more care. They must be mounted upright so the electrolyte won’t drip. Mainly sulfuric acid, the hazardous electrolyte can quickly eat through skin and clothes, and when mixed with seawater, it generates equally hazardous chlorine gas. In case of contact, immediately flush the area with clean water.

Flooded batteries must always be topped off, because exposed plates soon become sulfated. As a battery discharges, a chemical reaction takes place. The lead dioxide (positive plate) and the lead (negative plate) both change to lead sulfate, and the sulfuric acid turns to water, which is why you shouldn’t store discharged batteries in subfreezing temperatures. When the battery is recharged, the water changes back to acid, and the lead sulfate changes to lead dioxide and lead. The uncovered part of the plates can’t be converted back to lead dioxide, which reduces the battery’s capacity. When the lead sulfate hardens, the battery won’t regain its original capacity even if you refill the cells.

Lead, lead dioxide and lead sulfate—the three main components of a lead acid battery—have different densities, and whenever one replaces the other, the expansion and contraction cause stresses that dislodge materials from the grids. As dislodged lead sulfate accumulates at the bottom, it can eventually short out the cells. Aggressive handling of your boat in rough seas could bounce your batteries around and shorten their life through the flaking and accumulating of material in the bottom of the cells.

Keeping batteries charged on moored boats can be a problem. However, photovoltaic cells can use the sun’s energy to keep the batteries charged. A specially designed regulator is required to keep the charging voltage within battery specifications. Some regulators also contain circuitry to periodically equalize the batteries by allowing a higher charging voltage to be applied to convert the lead sulfate back to lead dioxide in all the cells. This is usually done monthly.

Special attention should be given to the electrolyte levels when this is done, as gassing is a result of equalization, and some of the electrolyte is lost in the process.

Topping off is very important in this operation. It’s easy to forget about batteries in out-of-the-way places, but your diligence will pay off in extended battery life.


Gel batteries

Completely sealed gel batteries are maintenance free, meaning you don’t have to add water. However, they cost more than flooded batteries. The sulfuric acid electrolyte has the consistency of jelly. Gel batteries can be mounted in any position except inverted, and they won’t leak if the case cracks. Because they’re sealed, gel cells can’t be rejuvenated by adding lost electrolyte. Therefore, they should be recharged by three-stage “smart” chargers to prevent overcharging. If a gel cell battery is overcharged, the water in the battery breaks down into hydrogen and oxygen through electrolysis. The resulting pressure is released by gas vents built into the battery, and there is no way of replacing the lost components.


Absorbed glass mat batteries

AGM batteries are the most expensive of the sealed, no-maintenance batteries, but they’re also the most rugged. These batteries have a fiberglass mat, which is compressed tightly between the plates, and the electrolyte is a paste (similar to primary flashlight cells) providing greater plate support and shock and vibration protection.

The lower self-discharge rate of about 3 percent a month, however, is a boon for those whose boats don’t have access to shore power.

Increased charge and discharge rates are also possible, providing increased cranking power. The difference between deep cycle and cranking batteries is mainly in the construction of the plates. Cranking batteries have many more thin plates, which increase the plate area contact with the electrolyte, providing increased current output. Deep cycle batteries have fewer and thicker plates, which provide lower constant current output.

Keep the batteries clean and dry, removing any battery salts with a solution of water and baking soda, taking care to keep the solution out of the flooded type vent caps. Add the solution to the terminals and case until the bubbling stops, and then flush the area with clear water. Make sure the connections are clean and tight. Your battery will reward you for your efforts.