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Recharge your battery knowledge


Here's all you need to know about leisure batteries

Jonathan Manning shares his know-how and offers real, practical advice for both beginners and those with more experience...

What does a leisure battery do?
A caravan leisure battery has three functions. Firstly, it powers the caravan’s 12V devices, such as the lights, water heater, oven, fridge, alarm and tracker.
Secondly, when the caravan is connected to the mains via an electric hook-up, the battery smoothes the delivery of power to the van’s electrical devices.And thirdly, a battery can store unused energy generated by solar panels. 

How can I check the quality of a leisure battery?
The National Caravan Council (NCC) has developed a Verified Leisure Battery Scheme, with clear labelling of a battery’s capacity. 
Category A batteries have a higher storage capacity and are designed for caravanners who tend to camp away from an electrical hook-up.
Category B batteries are for caravanners who typically stay on pitches with an electric hook-up, but also need greater power for devices such as motor movers.
Category C batteries are designed for use over a short period of time to provide power for basic, low-demand equipment. 
W thencc.org.uk

Do I need more than one leisure battery? 
This depends on how long you will be caravanning ‘off-grid’ and the electrical devices you intend to use. The longer you spend between electric hook-ups, the greater the need for a second battery (they retain their charge well, when not in use). Remember, however, that you will need space to store and secure the battery outside the main living area of the van, and that a second battery will add significant extra weight, reducing your available payload.

What’s a starter or cranking battery?
Think of this type of battery as Usain Bolt, capable of delivering a blistering surge of power to kickstart a vehicle engine. 

What’s a dual-purpose battery?
A hybrid of a starter battery and a deep-cycle battery, a dual-purpose battery can power the short-term intensive demands of devices such as a motor mover, and also cope with the long-term, lower energy demands of smaller appliances.

What’s the difference between a car and caravan battery?
A leisure battery has significantly thicker lead plates than a car battery, to contend with its charging and discharging cycles. As a rule of thumb, the heavier a battery, the more lead it contains and the better suited it will be to caravanning. 

What size of battery should I buy?
If you are replacing a leisure battery after several years of successful use, then replace like-with-like.
If you are buying a leisure battery for the first time, consider what you need it for (see the NCC ratings, point 2). Typically, the higher the ampere/hour (Ah) rating the longer a battery will last between recharges, and the longer its life. Remember, too, that its dimensions need to fit physically where the former battery was housed.

What’s a deep-cycle battery?
Think of this type of battery as Mo Farah, capable of delivering lower power but over a much longer period. This type of battery can be heavily discharged without damaging its recharging capability. Many batteries should not be discharged below 50% of their capacity, but a deep-cycle battery can take this figure to 80% 
and more.

When should I recharge a battery?
For most lead acid batteries, it’s important to recharge when the battery is at 50% of its capacity. Otherwise, the lead sulphate will crystalise on the lead plates and prevent future recharging. Forget about ‘battery memory’ associated with mobile phones – it doesn’t apply to lead acid leisure batteries. If you recharge every time the battery sinks to 75% of its capacity it will last longer than if you recharge when it is
at 50%. 

How can I measure the state of charge in a battery?
The control panel in most modern caravans will display the condition of the battery, although it’s not always the most accurate indicator of charge. For a more precise reading, use a hand-held voltmeter (from under £10 on amazon.co.uk), but be sure to turn off all electrical appliances beforehand (including any tracker or alarm system and even the clock on the microwave!). Try to avoid taking a meter reading immediately after recharging a battery, as this risks an unduly high reading.

What charge reading should I be looking for?
As a general guideline for a 12V battery, a voltage of 12.7 indicates 100% charge; a voltage of 12.4 is about 75% charge; and 12.2V is approximately 50% charge.

What’s the best method to recharge a leisure battery?
A long, slow trickle charge is much better than a high-speed boost charge. 

Can I overcharge a battery?
Yes, overcharging will lower the level of electrolyte in a battery, and in sealed batteries this cannot be topped up. If the battery feels hot or smells of rotten eggs (sulphur) while recharging, it’s a clue that it’s being overcharged. Investing in an ‘automatic’ or voltage-controlled charger will prevent this from happening – once the battery is fully charged, the unit will then switch off and subsequently only apply a light trickle charge to keep the battery topped up.

How should I maintain a leisure battery to prolong its life?
If your battery is an ‘open’ model, remove the vents and check the level of electrolyte in each cell at least once a year. The fluid should completely cover the lead plates – if not, top up with de-ionised (not tap) water – Tesco sells a 2.5-litre bottle of CarPlan De-Ionised water for £1. Battery makers publish guides as to the ideal electrolyte level. There is no way to top up a sealed battery, but as with all batteries, you should make sure you clean the battery terminals and connectors, and then apply Vaseline or any petroleum jelly to the connectors. Finally, it’s important to keep batteries properly charged to protect their performance. Through winter and when a caravan is in storage, recharging via an automatic charger will keep a battery charged up without over-charging. Alternatively, remove the battery from the van and store it in a well-ventilated room, checking its power levels periodically. Remember that security devices such as a tracker and alarm may rely on battery power, so check before you remove the battery from your van.

Are leisure batteries dangerous?
As a vicious corrosive agent, sulphuric acid demands respect, even when it’s sealed in a leisure battery. Make sure that any gases can escape into the open air, and not the living quarters of the caravan. Battery gas is flammable and explosive, so don’t smoke when you’re near a battery. Likewise, always wear safety goggles and gloves when topping up the electrolyte with de-ionised water. Choose good-quality clamps to connect to the battery terminals, and check these don’t rust over time. As when recharging a car battery, always disconnect the negative cable first, and reconnect it last.

What impacts on a battery’s performance?
Leisure batteries lose their charge more quickly in the cold. Bear in mind that official amp hour (Ah) ratings are based on an ambient temperature of 25°C, which the mercury rarely reaches in the UK. As a rule of thumb, for every one degree fall in temperature below 25°C, a battery suffers a 1% decline in performance. It’s useful to remember this in winter, when batteries face the double-whammy of colder temperatures and increased demand from caravan heating and lights if there’s no electric hook-up.

Which battery is best for use with solar panels?
An AGM battery is especially efficient at converting the electricity generated into stored energy.

How long should a battery last?
This all depends on the quality of the battery in the first place, as well as its use and how it is cared for. A better measure is the number of recharge/discharge cycles, which can span from 200 to a claimed 1500-plus for lead crystal batteries. 
A well-maintained battery should last from two years to longer than five years.

How do I know when to replace a battery?
When you find yourself having to recharge the battery ever more frequently with no extra appliances plugged in, it’s time to bite the bullet and buy a new battery.

How much should I pay?
Prices vary hugely depending on the capacity of the battery (see the NCC ratings in point 2), the technology (lithium-ion is eye-wateringly expensive, and up to 20 times more expensive than the cheapest lead acid battery), and brand. Buying the appropriate NCC class of battery for your caravanning should give you a decent 'whole-life' cost.

Useful contacts
Numax manbat.co.uk
Exide  www2.exide.com
Halfords halfords.com
DBS Energy dbsleoch.co.uk
Optima optimabatteries.co.uk 

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