Understanding and Using Marine Batteries
by Herb Allen
The difference between automotive and marine batteries is the divergence between night and day, Dolly Parton and Twiggy, or a shotgun and a rifle.
Let's face it, batteries are built differently.
Anglers who depend heavily upon electric trolling motors to move along a grass line or hop from one point to another will be better served by learning a bit about battery basics.
Probably many of us at one time or another have used our car battery to supply power for electric trolling motors, and then cussed when the automotive unit failed to hold a charge after a trip or two.
The reason is because car batteries are designed to supply short bursts of cranking power at approximately 300 to 500 amperes until an alternator can take over.
They're more suited for starting power than staying power. Marine batteries pull anywhere from 5 to 25 amperes whenever they are used to propel a boat. As a result, power is nearly exhausted after several hours of fishing.
A vital attribute of a marine battery used to supply power to a trolling motor is in its ability to bounce back. A good marine battery is designed to be charged and recharged, again and again, to full power, whereas a car battery is blueprinted for a different purpose entirely.
Marine battery plates are 15 percent thicker and the active material denser than those in an automotive unit.
Because car batteries need a fast energy flow, its plates are thin and the active material is porous, a circumstance that causes car batteries to deteriorate rapidly when repeatedly discharged since the active material drops from the grids, eventually destroying the battery.
Marine battery plates are reinforced with an interlocking web of glass fibers to hold the active material on for extra durability.
Like car batteries, marine units come in several sizes.
When selecting a marine battery, the first thing we should do is decide upon what our average discharge rate will be.
For example, an electric trolling motor will average 10 to 15 amps at medium speed. Assuming that we'll average 12 amps with our trolling motor while on a lake, how long should we expect a small and a large marine battery to continue delivering power?
A small, deep-cycle battery will probably provide about 5.3 hours of continuous power while a larger unit will perform well for about seven hours.
Both car and marine batteries will give us longer, more dependable and trouble-free service with proper care. We'd suggest these simple maintenance procedures:
1. Check the level of electrolyte frequently and add tap water to cover the plates, but avoid overfilling;
2. Keep terminal connections and cables free from corrosion by cleaning them with a wire brush and then coat them with a heavy-bodied mineral grease;
3. Fully charge the marine battery after each use;
4. When not in use, store your marine battery--fully charged--in a cool, dry place. If stored for several months, recharge it every 60 to 90 days;
5. Keep in mind that too small a charger will require more time to fully recharge a battery. A 10-amp charger will do the job twice as fast as a 5-amp model;
6. Don't overcharge the battery. Prolonged periods of overcharging will damage the unit by destroying the plates and "boiling off" the water;
7. Use a simple, inexpensive hydrometer for accurately determining the percentage of charge in a battery.
