The majority of modern motorhomes come with two batteries. The first – the vehicle battery – does the same job as that fitted to a normal car, providing power to start the vehicle, then keep the lights, horn, radio, heater and so on operating as you drive.
The second battery is the ‘leisure battery’. In a motorhome, this powers 12V electrical systems in the living area, such as the water pump and lighting. If either battery fails, your trip could be ruined, so it pays to know how to keep them in tip-top trim.

How they work
Having a basic idea of how batteries work will help you to keep them fit and healthy.
A fully-charged battery is essentially a plastic bucket full of sulphuric acid mixed with water (electrolyte) with two types of metal plates immersed in it. Electricity is produced as the result of a chemical reaction inside the battery.
Electricity flows from the battery as soon as those two metal plates are connected to an electrical circuit. Creating electricity in this way causes another chemical reaction, and the result is the formation of water in the battery, which dilutes the acid. When the battery is charged, the reaction is reversed again, the acid regains its strength and the battery voltage is restored.
The discharging and charging pattern is called a cycle. The number of cycles that a battery can complete, and the speed at which it does them, help us to determine how a battery can be used. The term ‘deep-cycle’ refers to a battery which gets significantly discharged before being replenished.
Battery performance can deteriorate for many reasons. Old age causes the metal plates to break up and their capacity for holding an electrical charge is reduced. More common is for bad maintenance to ‘kill’ a battery. Leaving a battery discharged, or with a low electrolyte level, allows sulphate crystals to bind and clog the metal plates. The effect is that the amount of charge available is reduced and the battery cannot perform properly. Frequent use of a good-quality charger and regular checking of electrolyte levels can minimise the risk of sulphation problems.
Battery additives can restore the chemical balance of a failing battery, and while these do re-invigorate them temporarily, it will inevitably need replacing.

 • The above is an extract from an article published in the May 2005 issue of Practical Motorhome magazine. The full article goes on to cover: Battery types, Looking after your battery, and the difference between leisure and vehicle batteries.

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