20
Self discharge
You should consider the self discharge if you leave the boat unattended for a long time.
Below 8° C the self discharge is nothing to speak of. The batteries will keep their charge for at least six
months. At 15° to 20° C, such as autumn in the Mediterranean, it will give no problem. At
temperatures over 20° C the self discharge has to be noted and over 30° C it must be supervised.
One month without charging should not be a problem, but three months can give you trouble.
Only when the cables are removed from the battery terminals you can be sure that all equipment is
disconnected, which is essential.
New and well maintained batteries will naturally stand better than old.
The best way to check the charging of the batteries is by measuring the specific gravity of the battery
acid. This is, however, best made by professionals. Battery acid is highly caustic.
If the voltage, after charging a few minutes, doesn't come up to 12.5 respectively 25 v or for an
extended period exceeds 14.2 respectively 28.4 v something is wrong and the charging must be stopped
until investigated.
A few words about consumption of electricity
We repeatedly get the question: How much power does the autopilot, the fridge or the heater use?
These questions cannot be answered as the consumption of an electric motor depends on how much it’s
loaded and for how long it runs.
When operating an electric windlass the main engine must be running.
The drain from the autopilot much depends on the sea condition and how you carry your sails. The
drain is however often overestimated.
A heater that is running day and night is naturally using more electricity than one that is shut down in
the evening and restarted in the morning.
A refrigerator is on the contrary best left on day and night. The thermostat setting, however, has a direct
influence on the power consumption.
A modern well equipped yacht offers every modern convenience and it should also be expected to cope
with the extended power consumption. However, on any boat the following cannot be disregarded.
Charge the batteries regularly and keep an eye on the power consumption. Then you will have no
problems.
The worst thing that can happen is that a battery or one battery cell is damaged without being noticed.
This will inevitably lead to damage to all batteries that are connected to the faulty one. Symptoms you
should beware of; Rapid loss of power by discharge and difficulties to reach full charge are as well as an
acid smell. Have the battery checked by a professional.
The second worst thing is a small lamp left on that will gradually drain your batteries to the last drop.
To avoid this: Always turn off the main switches before you leave the boat for some time. Or if it’s for
a longer time: disconnect the cables directly on the batteries.
Larger boats are often fitted with a battery controller. On this instrument you can see how much
electricity is going out or in and also see how much each consumers differ. It also shows how many
ampere hours that have been used or charged into the batteries. This is the best way to get familiar with
your electric balance.
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