A boat is equipped with a battery to start the engine and in some cases an optional generator. There is also a “house” battery bank that powers accessories.
These batteries have an operating voltage range of between 11.8V and 13.8V to maintain their rated output and life cycle. As items draw voltage down it must be replaced. This is done while plugged into shore power through a battery charger, while motoring through output from the alternator, and at any time the generator runs again through the battery charger.
There are three major types of batteries: flooded wet cell, gel cell, and AGM (absorbed glass mat). Each has its own unique characteristics regarding operating voltage range, discharge capacity, maintenance/service frequency etc.
The most popular batteries that are supplied on boats are the flooded wet cell type; these are like the battery in your car. Unlike your car however where after starting the engine it runs and so continuously is replacing the energy that was used. On your sailboat after your engine is shut down any combination of refrigeration, power winches, windlasses and bow thruster operation, electronics, lighting, radios and other items requiring power draw down the batteries. Your boat is fitted with a gauge that indicates the current voltage level and current draw.
There is an audible/visual alarm that occurs once the voltage drops close to the point where batteries if not recharged can become
irreparably damaged, (11.5v)
. Although many consider this audible warning annoying it must be acted upon as soon as practicable or your batteries will have a reduced capacity and shortened life. Additionally in the attempt to “recover” from this state of over-discharge charging circuits may need to run for extended periods that result in fluid loss requiring additional maintenance. Do not continue to operate your boat following the alarm without addressing the need to recharge. If you find that this alarm occurs with great regularity speak with your dealer about increasing battery capacity and/or increasing charging potential.
Advice for maximum battery service life:
- Minimize operation of your boat following hearing the low voltage alarm. Run engine or generator with battery charger.
- Keep your boat plugged in with the charger on anytime while at the dock.
- Check battery fluid level at least once per month, even on so-called maintenance free batteries.
- Have your batteries (individually) “load tested” once per season.
- Fully charge your batteries before storing your boat for extended periods.
- Remove the ground (black) and the power (red) cables from the engine start and house bank for winter storage. Check electrolyte level and charge monthly, if not possible follow suggestion #7.
- Remove batteries from boat and store in reasonable temperature when stored for more than 6 months. Check charge or leave on trickle charge if possible.
- Reinstall and always gently charge batteries following extended storage.
- Consider adding additional battery capacity to minimize overall voltage drain on battery bank.
- Consider alternate charging systems such as wind, solar, towing generation.
- Keep refrigerator full of high density materials such a liquids.