An Introduction To Leisure Batteries

Leisure Batteries

Whether you have a propensity for sites with electric hookup, or not, a decent leisure battery is an essential piece of kit to have integral to your on board electrical system.

There is plenty of information available, online, for those who wish to check it out, concerning the technical specifications and construction of the various battery types, however, in this guide, we will, simply, be looking at the basics of how they work, how to look after them, and the best ways to recharge them, when we need to.

Whilst it is, indeed, possible to operate 12v lighting and equipment in our camper, without a battery, using the on board power supply unit (PSU), this is far from ideal, particularly in the longer term (which is surprising, when you bear in mind that most manufacturers supply new units without a leisure battery installed, as standard).

This is because a typical leisure battery performs two main roles;

Firstly, it provides an independent 12v power source, for those times when electric hookup simply isn’t an option, and, secondly, even when EHU is provided, the battery sits between the transformer, in the PSU, and the rest of the 12v system, smoothing any spikes and other irregularities in the supply.

It is a common misconception that standard leisure batteries and standard car batteries can be interchanged, and many see the latter as, potentially, a cheap alternative to the former. Unfortunately, this is not the case, as they operate in totally different ways.

A standard vehicle battery rarely, if ever discharges to any great extent. It is used to provide the high power surge, required to start an engine, and then, immediately, begins to re charge again, via the vehicle alternator, as the engine continues to run. A leisure battery, on the other hand, has no need to provide such a surge, and is used to provide the more consistent power output required for running 12v lighting and other appliances.

A leisure battery is far more likely to be run for a period of time before being recharged, and it is this process of charging and discharging over a longer period that is know as deep cycling. Whilst vehicle and leisure batteries are interchangeable for short periods of time, neither will operate as efficiently or last as long if it is not used for its designated purpose.

Leisure Battery Options

Most leisure batteries are of the lead acid type. These consist of a series of six compartments, containing a number of positive and negatively charged lead plates. Each of these compartments provides an output of 2.12v, with a total output, for a fully charged battery, being 12.7v (in fact, contrary to popular misconception, a leisure battery with an output of 12v will, actually, be pretty much fully discharged).


A Typical Lead Acid Battery

Leisure batteries tend to be measured in terms of Amp hours (Ah) with most ranging from around 65Ah up to around 110Ah. Obviously, a 110Ah battery will last longer than a 65Ah one, but, of course, will, also, take longer to re charge. The simple rule is to go for the largest specification battery you can afford, although, for some, size may be a limiting factor there, if they only have a smaller dedicated battery compartment.

As the rating of a leisure battery increases, the thickness of the lead plates, internally, also, increases, meaning that a 110Ah battery can be quite a bit larger, and heavier, than a lower specification one, so we should, perhaps, amend that rule to; go for the largest specification one you can afford, provided it will fit in your battery compartment. To make things a little easier, leisure batteries are now graded, in accordance with their performance levels; as follows:

  • Category A. As the name implies, these are the top end batteries, with the highest specification, and are designed for those who use their units often, without electric hookup.
  • Category B. These are aimed at those who use EHU a lot more, but who, maybe, need a little extra power, occasionally, perhaps, to power a motor mover or similar.
  • Category C. These are the lowest spec. batteries, and are mainly used where 12v requirements are minimal. They also help smooth out the power supply from the central PSU, in the same way as their larger siblings.

Battery Performance

As well as the Ah rating, there are a number of other factors that will affect overall performance and discharge times. These include;

  • Temperature. Just like Butane gas, batteries will suffer a loss in performance as the temperature drops. In fact, a battery will, on average, lose 1% of its performance for every degree Centigrade of temperature drop. The specified Ah rating of any given battery is its equivalent rating at an ambient temperature of 25 degrees C. A drop of 20 degrees, from this, will result in a drop of, approximately, 20% efficiency.
  • Age. This is another key factor, with batteries losing efficiency over time. Although life will vary, the general consensus is that the average leisure battery will have an optimum life expectancy of around five years.
  • Rate of usage. Sounds like common sense, but it isn’t simply a case of a 100w appliance draining a battery twice as fast as a 50w one. The higher draw rate of the 100w appliance will, actually, further impact on the overall discharge time of the battery, which will last less than half the time it would have with just a 50w appliance connected.
  • Charging regime. A battery that is correctly maintained at an adequate level of charge will, inevitably, last a lot longer than one which is allowed to discharge too much, for too long, and is not adequately recharged.

It is very important to keep a leisure battery charged correctly (more on that below) and its current state of charge is relatively easy to measure, using a simple Volt meter. As mentioned above, it would be, you would think, common sense to assume that a fully charged battery would operate at 12v, but this is not the case. Due to its 6 compartment composition, a fully charged leisure battery will, actually, operate at 12.7v. The key stages of discharge can be summarised as follows:

                                             Charge Level                         Volt Meter Reading

                                                     100%                                                   12.7v

                                                       75%                                                    12.5v

                                                       50%                                                    12.4v

                                                       25%                                                    12.2v

                                                 Discharged                                       12v or less

Remember, when taking readings, to disconnect as many appliances as possible, as each connected appliance will affect the accuracy of the readings. It is also prudent to wait for three to four hours after charging, to allow the charge to ‘settle’.

Battery Care & Maintenance

Batteries are, in the main, relatively, low maintenance. It used to be common practice to have to top up lead acid batteries with distilled water, to ensure the lead plates are covered. This may, on occasion, still be required, however, you tend to find, with modern batteries, and charging systems, that this is only, normally, required if a battery has been charged, for a while, at a very high rate, which can cause the electrolyte to over heat, and ‘boil off’.


A Dedicated Battery Compartment, Complete With Retaining Straps, Storage Tray and Correct Terminal Connectors. The Door Will, Also, Incorporate Vents To Allow The Battery Gasses To Escape.

Any leisure battery should be firmly secured in place, ideally, in a vented battery locker, in order to allow for any escaping gases, which can be emitted during periods of higher charging levels. This compartment should have high quality battery connectors. The crocodile type connectors, common on many battery chargers, are not suitable for long term connection, as they can move, causing sparks, which, in extreme cases, can ignite the gasses venting from the battery.

(It is not unknown, also, for these gases to trigger carbon monoxide detectors, in enclosed spaces).

Lead Acid Battery Sulphate

Typical Sulphation Of Lead Plates

A leisure battery must be kept at an appropriate level of charge.

If it is allowed to drop below 50%, it is unlikely it will achieve 100% charge ever again. If it is allowed to discharge fully, for any period of time, without recharging, then the process of sulphation will occur.

This is when white powdery deposits of lead sulphate accumulate on the lead plates.

Eventually, these begin to crystalise on the plates, rendering them unusable. This process is generally considered to be irreversible, and the battery will need to be replaced, although there is a possibility that it may be partially revived through the use of a ‘pulse charger’. This is one of a variety of means of charging a leisure battery, and these are looked at, in more detail, below.

Lead acid batteries will have inspection caps, which allow the user to check electrolyte levels and top them up, with distilled water, where necessary. Although a relatively straightforward procedure, it is wise to take precautions when undertaking this task. Protective clothing and glasses should be worn. Battery gas is highly explosive, and, if a battery does explode, the acid, inside, can damage clothes, as well as eyes, skin and other tissue, so just be aware of any flames or sources of sparks, nearby (including inadequate battery connections).

It never does any harm to apply a protective layer of Vaseline to battery terminals, either, and to keep an eye on them, to ensure they remain clean, and free of rust.

Battery Charging

As already mentioned; it is vital that a leisure battery is maintained at an appropriate level of charge, to avoid permanent damage to that battery.

It is, perhaps, worth mentioning that on board PSUs are designed to perform a number of functions, including powering the 240v system, the 12v system (via a transformer) and charging the battery. Although the more modern ‘intelligent’ chargers are going some way to improve this, the modern PSU is a bit of a jack of all trades, and, as such, is not as able to fully charge a leisure battery as the more dedicated battery chargers are.

It is never a bad idea to remove a battery, periodically, in order to charge it with a proper leisure battery charger which will help to give it that extra boost, to ensure it remains in top condition. This is particularly relevant over the Winter period, especially if the camper is laid up in storage for a number of months.

It’s important to remember that lead acid batteries will suffer from a degree of internal leakage, which means that, even if they are disconnected from the 12v system completely, they will still require a top up recharge every six to eight weeks, in order to prevent them from dropping below charge levels likely to cause long term damage. In this case, 50% is considered to be the minimum safe level of charge before the battery must be recharged again, if some degree of damage, or loss of function is to be avoided.

If time is not an issue, then a slow charge, over a longer period of time, is universally accepted as being the preferable option, as opposed to a more rapid charge over a shorter period. A charger running at around 4 or 5 Amps is, generally, considered to be an acceptable rating for a charger of this nature. How long a recharge will take will depend on a number of factors, including, of course, how discharged it was, in the first place. An easy way to get around this is by the use of a ‘smart’ charger, which can be left permanently attached to the battery, maintaining its charge at the optimum level.

There are four main types of battery charger we can use;

  • On board charger
  • Standard charger
  • Semi-automatic chargers
  • Automatic chargers

On Board Charger

These have, largely, been covered above, and are part of the on board PSU, rather than being a dedicated charger in their own right. If the charge, from these units, was too high, it would ‘boil’ the electrolyte solution in the battery, causing ‘gassing off’ which is not ideal, as it means that not only will the battery need topping up with distilled water every so often, but, also, it will be emitting potentially explosive gasses, which is never ideal, at the best of times, and can, also, result in the false alarming of certain carbon monoxide detectors.

Acer Image

The PSU 2005 Is a Typical PSU, And Is Found In Many Folding Camper Models, Including Much Of The Pennine Range.

In order to avoid this over charge, on board chargers are rated so as to only charge a leisure battery to around 80% of its capacity at any given time.

More modern ‘intelligent’ on board chargers are able to increase this to 90% of capacity.

The theory is that the battery charge can be ‘topped up’ using the vehicle alternator, whilst in transit.

This is something that many aren’t aware of, and it may, just, be a factor in deciding whether or not to opt for single or twin / euro electrics when installing a new tow bar. Going for option 1 may mean that you arrive on site with a battery that is considerably less charged than it could have been.

Standard Charger

These are more akin to the old style chargers of a few years ago, and have, mostly, been replaced by automatic or semi-automatic chargers in the modern world. They deliver an unregulated charge, which can rise to very high levels as the battery becomes close to being fully charged. For this reason, they should not be used unless closely monitored.

Semi-Automatic Chargers

These are another, relatively simple, charger but they are designed to cut out once the battery reaches a pre determined limit. The idea being that they are able to provide a full level of charge, but without causing significant gassing within the battery. They, basically, achieve the same as the on board battery, only with greater efficiency and higher charge levels.

Automatic Chargers

I’m sure it will come as no surprise to learn that these are considered to be the best type of charger to use. They are, also, the only ones that can be left connected to the battery over a prolonged period of time (although low power ‘trickle chargers’ can, also, be left on for relatively long periods, but they are far less controllable than an automatic charger). Rather than, simply, cutting out at a specified  level of charge, these units will charge the battery in a number of different ways, depending on the stage of charging achieved.

Initially, the chargers enter the ‘constant current phase’ where a constant current is applied to the battery until a pre determined terminal voltage is achieved. Next the charger enters the ‘constant voltage stage’ wherein the voltage is maintained at that level, whilst the current drops, until the current stabilises. The final stage is the ‘float mode’ where the battery is kept at a constant voltage of around 13.6v, thereby ensuring the battery is maintained at optimum charge level, at all times.

In addition to their more standard features, some automatic chargers, also, have a number of enhanced features. An example of this is ‘pulse mode’, whereby the charger senses that sulphation has occurred in the battery, and delivers a controlled series of high frequency pulses which are designed to break down the lead sulphate crystals, thereby restoring some of the useful life of the battery. Another such feature is the ability to monitor the temperature of the battery, and regulate the charge supplied accordingly. This facility also helps to prevent over heating of the battery.

Charging Without EHU

In our previous article; Making The Most Of Life Without Electric Hookup, we looked at some of the options of charging a battery, whilst camping without the benefit of EHU. The three main options here are;

  • Solar panel
  • Wind turbine
  • Portable generator

The pros and cons of each option are covered, in more detail, in that earlier article. Feel free to check it out at your leisure.


About Alan Young

MD and owner of the Woodhurst Group, including Praxis Accountancy Limited and Blue Sky Recreation Limited. Also Commercial Director of The Sky visor Group
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