Sammy FairclothSee other Advice articles filed in ‘Electrics’ written by Sammy Faircloth
Leisure and car batteries may look very similar, but are quite different in performance and how they are made. Your car battery is intended to provide a burst of energy to start the engine, whereas a leisure battery releases a lower level of energy, which is intended to work over a longer period of time. Unlike a car battery, once a leisure battery fully discharges, it cannot be recharged.
Another key difference is the size of the plates - starter batteries have numerous thin plates, whereas leisure battery plates are three times thicker and coated in a different lead oxide mix.
The separators, which keep the plates apart, are similar, but the leisure battery is lined inside with a sheet of fibreglass packing, designed to keep the lead oxide in place when the battery is cycled (discharged).
Starter batteries use the term Cold Cranking Amps (CCA) on their label, which is a rating used in the battery industry to define a battery's ability to start an engine in cold temperatures. Leisure batteries show Ah capacity, not CCA, as they are not intended to be used to start a vehicle.
What does a leisure battery do?
Leisure batteries have two jobs: they supply 12V DC electricity to run your 'van accessories, and smooth out any irregularities in the 12V power from a motorhome charger when hooked up to the mains supply.
If you tour in remote locations and go off-grid, or enjoy the many rallies that take place throughout the year, it's important to have a fully charged leisure battery as a power source. Even if you use a solar panel to provide some power, you still need a leisure battery to store any electricity generated.
Types of leisure batteries
The five main types are as follows:
Open lead acid: Known as a wet or flooded battery, this can be accessed for maintenance, which prolongs its life. Access is through screw-in vents, for which special tools should be used to prevent damage. These batteries are topped up using de-ionised water.
Sealed lead acid: These are similar to open batteries, except they cannot be accessed for maintenance and are often referred to as 'maintenance free'. They aren't completely sealed, however, as a vent is provided for gas escape in the side of the lid, and tipping will allow acid to escape.
Absorbent glass mat: On the outside, this looks similar to a flooded battery, but it incorporates absorbent glass mat (AGM) separators. This fine white fibreglass material is rather like blotting paper, in that it soaks up and retains the electrolyte (acid). This battery should never be opened. Although these spill-proof batteries have a longer life and better starting performance, they can be twice the price of a standard wet leisure battery.
Gel: These use a gel electrolyte and do not need to be kept upright. They are seldom used in the UK and are very expensive (twice the price of an AGM). They have very poor starting performance, but excellent durability (about twice that of an AGM).
Lithium: These are very lightweight, compact and powerful. It is possible for some to come with Bluetooth, so you can check the status of the battery on your smartphone. Claimed performance levels are excellent; but they are still relatively new, so longevity is unproven, and they are very expensive.
What size battery do I need?
To establish the correct size of battery for your motorhome, consider how you intend to use it. Do you go off-grid, or do you always use mains hook-up? How often do you use your 'van?
To put this into context: say you have a 50Ah battery and you found it lasted for 200 cycles. If you replaced it with a 100Ah unit, you'd expect to get 400 cycles (if you did the same amount of work) - but in fact, you are likely to achieve 800 cycles. This is because the cycle depth is much shallower, so life expectancy is much longer. The deeper the discharge, the shorter the life.
There are huge variations in leisure batteries' quality, performance and price, so in 2016, the NCC introduced its Verified Leisure Battery Scheme to grade the different types.
The aim was to help consumers make informed choices about the type of battery that would suit their needs.
Batteries are tested for performance and graded as follows:
- Category A: These are aimed at people who frequently use their motorhome without electrical hook-up.
- Category B: For those who regularly use sites with electrical hook-up, but require a greater battery capacity.
- Category C: These are aimed at 'van owners who only require their battery to support the basic operation of their habitation equipment for short periods away from electrical hook-up.
For further assistance in selecting the right leisure battery for your particular requirements, visit the NCC website.
Maintain peak performance
The most important point to remember about leisure batteries is not to leave them in a discharged state.
With this in mind, I would suggest investing in a handheld voltmeter, so you can make a proper assessment of the state of your battery - meters in some 'vans might not be so accurate.
A guideline to understanding the Voltmeter reading is as follows:
- 12.7V to 12.8V......100% approximate charge state
- 12V or under........Discharged
It's worth noting that performance between charges deteriorates as the battery gets older, and that the colder the weather is, the harder the leisure battery has to work.
With sealed batteries, there is very little to do in the way of maintenance. Keep the battery charged, regularly check the state of charge, and clean the terminals and coat them in petroleum jelly or WD40.
Open batteries need to be checked at the beginning and end of the season for water usage. Remove the vents with a special tool or a wide-bladed screwdriver, being careful not to damage the slots. The electrolyte should cover the plates by about 15mm; if not, add de-ionised water.
During winter, of if your 'van is kept in storage for long periods, regularly check that the battery is fully charged. If it is left to go flat, this will result in a chemical reaction - called sulphation - taking place, which is irreversible unless caught early, and even then can only be repaired by specialists.
Unfortunately, many batteries on the market that are claimed to be leisure batteries are in fact starter batteries (used for cars) in disguise.
So if you are shopping online, do be careful what you buy. For added peace of mind, look out for the NCC Verified Leisure Battery Scheme logo.