Considerations when choosing batteries for your yacht

08 January 2021

Batteries are a critical part of the inventory of a yacht. Without batteries, we have no electronic means of communication, no navigation or domestic lights, no watermaker, no means of starting our engine and no navigational equipment. We also have no electronic bilge pumps, water pumps or anything electrical.

The standard battery set-up for the average small yacht might comprise 2 x 12v domestic batteries and 1 x engine start battery. The domestic batteries are designed to supply constant charge over a long time period. Engine start batteries are designed to give a shorter but more significant ‘shunt’ capable of turning over the engine and/or generator. 

Larger sailing vessels are usually based on a 24v system. In large part, this is so that longer wiring runs can be efficiently used to deliver power throughout the vessel. This requires 12v batteries to be wired in series and parallel for the domestic bank. The engine battery will usually remain linked to a 12v battery.

In many cases, yachts use sealed lead-acid batteries. The benefit of sealed batteries being relatively low maintenance. Other yachts use lead-acid batteries which allow top-up. Lead-acid batteries have very low energy to volume and energy to weight ratios but it has a relatively large power to weight ratio and as a result, can supply huge surge currents when needed.

Batteries are generally rated by the power they can store in amp-hours. When establishing how much power you need, you’ll need to calculate your maximum and average power requirements. Then you’ll need to look at the time it takes to charge and the spec of your vessel’s alternator and mains battery charger. The temperature and environment in which you will be sailing also need to be taken into account.

Nowadays, a new generation of lithium batteries brings great benefits. They are much lighter than lead-acid batteries and can be charged quickly. Furthermore, if the batteries run down completely they are not damaged! Unlike lead-acid batteries which can be entirely destroyed by complete discharge or poor charging discipline. Unfortunately, they are also still very expensive at this time.

In an ideal world, a 24v bank of lithium batteries linked to an alternator, mains charger and solar panel/wind turbine might be a great option but, like everything else, one has to consider the cost/benefit. Either way, the lightness of the battery makes siting of the batteries less critical, where weight must be kept as low as possible to improve stability and centre of gravity.

In any event, the battery bank should be properly stored in secured battery boxes in accordance with the manufacturer’s installation instructions and all wiring should be properly fused.