Battery problems at sea are not uncommon. Sea Start, a marine breakdown service, attends more than 2,000 call outs each year, mostly for electrical faults. These can cover a whole multitude of issues such as starter motors, alternators, fuses, engine management system, switches, corroded contacts and, of course, batteries.
Batteries are important – without them you cannot start the engine or have any lights or navigation. The electronic engines fitted on modern boats are battery dependent, both for starting and to keep them running.
A fully charged lead acid battery should read around 12.65 volt when measured by a voltmeter. A flat battery will read 12.00 volts – 11.65 volts or less. When the batteries are being charged by a battery charger or engine alternator the voltage should read a voltage of between 13.5 volts and 14.5 volts.
IN GOOD ORDER?
Good voltage is not always a sign that batteries are in good order. You may have the correct voltage but due to poor electrolyte or plate sulfation the power (amps) may be down. To keep the battery healthy, check the electrolyte level is above the plates, and top up with distilled water only. Note, lead acid batteries contain a mixture of sulphuric acid and distilled water so any spillage or splash can be very dangerous. Goggles are a must!
When batteries are being charged they give off small amounts of hydrogen gas. However, if the alternator regulator fails and overcharges the battery, the discharge of hydrogen will be much greater. Hydrogen is highly flammable and potentially dangerous. The charging voltage should never go above 15 volts on a standard 12 volt system.
Another cause of the battery overheating is an internal short within the battery, which can occur when a battery runs dry and the positive and negative plates inside buckle and touch each other. Signs of overheating can be a smell of rotten eggs, loss of battery power or high voltage on the engine voltmeter.
If this happens avoid all flames and vent the compartment. Do not disconnect the batteries at the terminals as this may cause a spark. Switch the batteries off at the isolator switch if necessary. Finally, leave the batteries to cool down before removing.
The life of a battery depends on many circumstances so Sea Start recommend that batteries are changed every three to four years and specific engine start batteries every three years.
There are two different types of battery:
DEEP CYCLE OR DOMESTIC – for use when small loads are needed for a long time e.g. navigation, lights, autopilot and instruments. These are constructed of thick high density plates and can be discharged to 50 per cent without harming the battery.
HEAVY DUTY/STARTING BATTERIES – these are used when large loads are needed for short periods of time e.g. engine starting, windlasses and bow thrusters. Constructed of thin plates closely spaced to get maximum surface area, any discharge to the battery must be restored quickly (recharged).