TIPS FOR THE CARING AND FEEDING OF MARINE BATTERIES
The first consideration for boaters is always to buy the right battery. Many boaters assume they need a deep-cycle battery. After all, a deep-cycle is a marine battery, right. Well, yes and no. There are actually several different types.
A true deep-cycle has relatively few, yet stout, grids . These batteries resist the damage caused by repeated draining, but don't produce as much cranking power as an automobile battery, which has numerous thin plates. Then, there's the dual purpose starting/deep-cycle battery that lies somewhere between the two.
To understand how to maintain a battery, you must know the enemies of long life.
Batteries stay healthiest when fully charged. Their biggest killer is being drained to zero percent. While deep-cycles are designed to resist draining, charging this type of battery after a complete drain decreases the unit's life.
When a battery discharges, the active material on both the negative and positive plates converts to lead sulfate. The plates become more a like in terms of their electrical charge, and the battery's acid, which conducts electricity between the two poles, grow weaker. This results in a voltage drop because the battery depends on the polarity difference between the two plates, as well as the acid's strength. During charging, the process reverses itself. Therefore, if a battery is left in a discharged state for a long period of time, the damage can be irreversible. If you run a battery down, it's important to charge it as soon as possible and not wait until the day before you go fishing.
The opposite, overcharged, can be even worse. This causes battery acid to percolate, which can then overflow or escape as gas through the vent, with resulting heat buildup, the plates will soften and shed the charging grid's active material, causing a dramatic decrease in productivity.
Cold temperatures are ideal for storing batteries. Heat accelerates discharge. A battery will retain its charge indefinitely at temperatures less than 37 degrees F. so leaving it our for the winter isn't a problem. The important thing is to make certain it's fully charged, because a deeply discharged battery's acid lowers a specific gravity similar to water and can freeze at temperatures near 10 degrees F.
Battery placement is another concern.
Most sterndrive boats have the batteries in the engine compartment, which is the equivalent of sending them to Death Valley for the summer. Boaters can counter extreme compartment heat by partitioning off the battery compartment with styrofoam. Make sure you have some ventilation, since batteries can emit flammable hydrogen fumes that accumulate and ignite if a terminal wire is loose.
You can get about three years of use from every battery, mainly by taking care of the basics. Check each battery's fluid level regularly, knowing that dry plates harden and become less effective.
If you find a battery to be low on fluid, refill the water level only high enough to cover the plates before recharging. Since the electrolyte solution expands during recharge, this will prevent overflow. When the charger switches to a lower amperage near the end of the recharging process, it's OK to add the needed amount of distilled water to bring the battery to its proper fluid level.