Narrow boat breakdown pt. 3 - batteries and electrics

Common misunderstandings around what battery to use; its electrical capacity, charging levels and lack of attention to electrical connections contribute to batteries and electrical malfunctions.


If you link a leisure rather than a cranking battery to your starter system you could be left without power when you need it most.

Leisure batteries and cranking batteries are designed for different requirements. The cranking battery is the same as fitted to most vehicles and designed to deliver a high output quickly, it discharges and charges back to full capacity quickly. A leisure battery is designed to deliver lower output continuously and therefore as long as it's charged regularly will maintain capacity. As a general rule, each battery in your battery bank will require two to three hours charging to get back to full performance once fully discharged, assuming that it is in good condition.

If the wrong battery is used, the sudden surge of power needed to start the engine can quickly drain capacity on a leisure battery and whilst regular charging helps to regain these levels, using this type of battery will eventually lead to battery failure.

It's worth mentioning that many 'leisure' batteries sold in the marine market are modified starter batteries and their performance, whilst suitable for owners who use the boat on a sporadic basis, can prove unreliable for more frequent users. For live aboard and frequent users it's worthwhile investing in true leisure batteries such as those provided by Banner.

Most people do not realise that each battery cell can affect the whole battery bank, and one of the best ways to prevent battery deterioration is to regularly check and top up the water levels in the cells (using de-ionised water). If one cell's water level drops to below 50%, it will affect the battery capacity and bring the battery bank capacity down to the same level, irrespective of how good the other batteries are. This is one of the best reasons never to mix and match batteries. Always replace the whole bank of old ones with new ones.

Similarly, battery terminals should not be forgotten - if they're tight and greased they'll deliver a good connection. It only needs one loose terminal to cause engine failure and usually the main earthing cable (connected to the engine bed) is the culprit.


On a similar vein, wires coming away or corroding is a common fault, so again, visually check and look for loose connections or disconnected wires before you journey and use a water resistant spray or petroleum jelly to stop damp getting into electrical components like isolators and block connectors.

Read more on narrowboat maintenance:

The basics
Preventative maintenance
Fuel and breaking cables
Cooling systems and alternators

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