DUNCAN KENT has been testing boats for more than 25 years and is a technical and features writer for nautical magazines, including YM
Should you ever suffer total loss of power, the obvious place to start troubleshooting is at the batteries. Older boats with several previous owners will have had many extras added over the years and, inevitably, some won’t have been installed to a proper standard, which can cause all sorts of problems when trying to track down a fault.
If your battery terminations are corroded or covered with acidic residue (often caused by lack of ventilation), loosen and remove all connected cables, taking care to mark their designation first. The key to easy troubleshooting is to label every cable indelibly, ideally adding this information to the boat’s wiring diagram.
Then, wipe clean the inside and outside of the battery terminals with a damp cloth, before lightly abrading with fine Emery paper (not wire wool) and smearing them with silicone grease before re-tightening each connection. As you do so, note that battery clamps are usually tapered, so completely loosen the terminal clamping bolts before putting them back onto the terminals, ensuring they mate together well. If there are too many connections made directly to the battery terminals, then complications can arise. A better method is to use positive and negative bus bars, taking a single cable to the bus bar from each battery terminal, with the appropriate large fuse in the positive feed. This will allow you to use proper crimped and insulated ring terminals, preferably the heat-shrink sealed type.
BATTERY FAILURE
If you are suffering from consistent low voltage, disconnect and separate the batteries, leaving each one to settle for a few hours before measuring the voltage
