John WickershamSee other Advice articles filed in ‘General caravan advice’ written by John Wickersham
Around this time of year, thousands of caravan batteries spark into life for the very last time. Naturally, it’s tempting to blame the product when it’s as flat as a pancake the following spring, in spite of the fact that its owner is at fault.
Much to many caravanners’ surprise, a leisure battery is not a ‘fit and forget’ component. It has to be treated with care and kept in a good state of charge. For example, if it’s left unused, it slowly discharges and some types lose power quickly.
If we relate this inevitable deterioration to the annual caravanning calendar, many owners seldom head off for a break in the winter. In consequence, their tourers are parked-up for a number of months and it’s not uncommon for a caravan to cease being used in September and then to go into hibernation until Easter. Unfortunately, caravan inactivity affects the condition of its tyres, brakes, couplings, water systems and leisure battery; it’s the battery we’ll focus on here.
Provided you own a good-quality leisure battery, continual attention helps it stay in good shape. There should be no reason at all why it needs to be dumped and replaced when the next season starts. But what must you do so it stays in good nick? And how can you ensure that it remains fully charged?
In this article, the advice concerns ‘wet’ lead-and-acid leisure batteries. Different charging and care guidance is applicable to gel batteries or absorbent glass mat (AGM) batteries.
As a starting point, you need to establish the existing charge condition of your leisure battery and a good way to do this is to take a voltmeter reading at its terminals.
However, this shouldn’t be done immediately after a charger has been disconnected because that merely shows an impressively high reading. In fact, it’s usually recommended to let a battery settle for at least four hours before taking a voltmeter reading. Accuracy is important, and another way to get false information is to check a battery when it is still coupled up in your caravan and is still providing power to:
- A clock
- A master control panel
- An electronic alarm system
- Other 12V components, such as a refrigerator control fascia (even though the fridge itself isn’t cooling) and a TV signal amplifier (even though the television is not in use)
Although none of these are ‘power hungry’ components, collectively they draw a small amount of electricity – thereby causing a battery voltage reading to be slightly reduced. To eliminate their interference, a common practice is to disconnect one (or both) of the caravan’s battery clamps.
Most caravan enthusiasts are fully prepared to purchase a good multimeter, which typically carries out a variety of electrical checks – one of which is to measure volts. Models with a digital liquid crystal display are especially useful and you can purchase meters for less than £20.
Of course, you may point out that many caravan control panels include a battery ‘condition’ meter, some of which use green/amber/red lights as opposed to a voltage ‘read-out’.
Either way, these devices are not usually as accurate as a purpose-made meter. For example, if the gauge is situated quite a long way from the battery, there can be a voltage drop and this becomes more acute if the diameter of the coupling cable is inappropriately small. Moreover, a light indication system doesn’t normally inform you of the exact voltage, as revealed in the next section.
Although we talk about ‘12V’ batteries, this description is only ‘nominal’ (that is, in name rather than in reality) and that’s misleading. For instance, if a leisure battery yields a 12V reading, it is considered to have reached a discharged state. That often comes as a surprise.
As a rough guide, if the voltmeter state reading is 12.7V or over it's 100% charged, if it reads 12.5V it's 75%, if 12.4V then 50%, if 12.2V it's 25% and if the reading is 12V or under, it is discharged.
Measuring your leisure battery’s state of charge is certainly important, especially if you’re about to put a caravan in storage for the winter. At the very least, it should be fully charged, but the situation doesn’t end there. For instance, are you aware of the following points?
- Battery manufacturers strongly advise that a battery be recharged as soon as its capacity falls below 50% of its fully-charged state.
- Power should not be drawn from a leisure battery when it drops to a completely discharged state – 12V or less. Allowing this to happen makes it virtually impossible to fully charge it again.
- If a van is unused for an extended period, the leisure battery must be kept fully charged. To keep your battery in this state, you may decide to purchase a purpose-made ‘maintenance charger’. Alternatively, some general-purpose chargers also offer a ‘maintenance charging’ setting.
- Never leave a battery in a discharged state. If recharging is delayed, a situation known as sulphation takes place in which a white deposit forms on a battery’s plates.
- In almost all instances, sulphation is an incurable condition. When it occurs, a battery is considered to have reached the end of its working life and is ready for disposal.
- On an unsealed lead-and-acid leisure battery, it is important to check each cell periodically to see whether its electrolyte is just covering the top of all the lead plates inside. Add de-ionised water to any cells that are low.
- Before inspecting a battery’s cells, ensure there are no naked flames or lit cigarettes nearby. It is also strongly advised that you wear safety spectacles during inspections.
In the light of this guidance, and presuming you don’t want to purchase a new battery at the start of every caravanning season, let’s see what your options are at the start of a long spell of storage.
Battery care in storage
If a time comes when you won’t be using your caravan for several months, you need to decide whether to leave the battery in situ in its purpose-made storage box or whether to remove it and keep it on a workbench at home for ongoing attention.
Making the decision might not be straightforward. For example, if your caravan is fitted with a 12V alarm or some kind of tracking device, removing your leisure battery is likely to disable them. What’s more, the conditions of your insurance cover may not allow you to cause an alarm system to become inactive.
On the other hand, you may put your caravan into a commercial storage site. It’s not usual for these facilities to provide clients with 230V hook-up for battery charging.
For this reason, many caravanners prefer to disconnect and remove the battery, whereupon it then becomes necessary to store it in a dry, warm and safe place. For many, that’s a shed or a garage, but it has to be kept well away from petrol cans and naked flames.
The battery must also be in a place with good ventilation, because in some charging situations, a battery can emit an explosive gas (a mix of hydrogen and oxygen) that rises and needs to be dispersed safely.
Be aware that there are different types of battery chargers. For example, the built-in models in most caravans do not yield more than a 13.8V maximum charge, whereas to revive a heavily discharged battery you need a higher output.
Battery manufacturers point out that most lead-acid batteries respond best when initially fed around 14.4V, which tapers off to a lower voltage level as the battery recovers.
Get the voltage right
Limiting a charger to an output of 13.8V recognises that when caravanners stay on a pitch and are hooked up to the mains supply, they will simultaneously be using 12V accessories.
Since most built-in battery chargers automatically run in the background, 12V accessories may be damaged if the charger’s output is too high. In reality, most 12V accessories can survive when operating at just over 13V, but that might not be the case if a charger is feeding 14.4V into a battery.
However, during a storage period the situation is different. For example, you should aim to start with a fully charged battery and the task then is merely to maintain it at that level. This can be achieved in several ways.
For a number of years, there have been mains-operated ‘maintenance chargers’ that provide a continuous low trickle charge for keeping a battery in a topped-up state. However, the latest maintenance products are more sophisticated than old-style trickle chargers because modern versions employ circuits that react to a battery’s condition and then deliver charging patterns to suit specific requirements.
For instance, if such a device notes that a battery has reached its peak, it switches off automatically even though it remains plugged into a mains socket. It switches itself on again when the charge has dropped.
In view of their ability to monitor the level of charge and react to it, these products are often called ‘intelligent maintenance chargers’. Not surprisingly, this versatility is also available in many of the chargers that also recondition discharged batteries rather than just serving their maintenance needs. In fact, modern electronic ‘intelligent’ chargers often have the ability to provide a regime to suit either wet lead/acid batteries or sealed gel batteries. Some include selection settings for starter batteries as opposed to ‘leisure batteries’. Needless to say, the subject of charger designs is a topic in its own right.
As far as a caravanner is concerned, different circumstances commend different strategies. Some owners keep a caravan at home and run a mains hook-up lead directly out to the van from a domestic socket protected by a residual current device (RCD). Others store a caravan elsewhere and bring the battery back home for attention over the entire storage period.
A few people have a large, 60-80W solar panel installed to provide an alternative supply to the battery. The only trouble here is that in the depths of winter, the hours of daylight are short, so the power yield is far less impressive than it would be in summer. That’s not very helpful because few people store caravans in summer.
So give this some thought and don’t join those owners who take no precautions and need a new battery when their touring resumes.