Caring For and Charging Your Leisure Battery

What is a leisure battery?

A leisure battery supplies power to the 12-volt appliances in your caravan, including the lights and any 12-volt sockets you may use to charge mobile phones or power 12-volt TVs. Your hob, oven/grill, fridge/freezer, heating, and hot water will work on a combination of gas and the leisure battery.

Can you use a Car battery as a leisure battery?

A regular car battery is designed to deliver a high level of power for a few seconds. In contrast, a Leisure battery is designed to supply a lower, constant amount of power over an extended period. Externally, car and leisure batteries may look the same - with both providing 12 volts - although there are significant differences in internal construction. Should you be wondering if leisure batteries need different chargers to car batteries, this is measured by each battery's amp hour rating and the rating of the charger.

Common mistakes to avoid to extend the life of your leisure battery.

With care, a caravan's leisure battery can last for many years. Without it, it could fail during its first caravanning season. These common mistakes often lead to premature failure:

#1 Over-discharging the battery.

A good quality lead/acid battery should tolerate discharge to 50% and be able to do so hundreds of times. This charging/discharging process is called a cycle. A healthy battery should show 12.7-volts or more when fully charged, but a 50% discharge doesn't mean it'll be operational until it falls to 6.35-volts. In reality, a 50% discharge could drop the voltage to 12.4/12.2 volts. This figure can be monitored on your caravan's battery meter, but turn off all appliances before checking.

#2 Partial or complete discharge.

Leaving your battery in a partial or complete state of discharge for more than a few days can lead to sulphation. Lead sulphate forms on the battery's plates during discharge, which converts back to lead/lead dioxide during the charging process. However, the sulphate crystallises if the battery is left for an extended period, making this process difficult.

#3 Dry plates.

Open lead/acid batteries require topping up from time to time. This type of battery is easily identified by the six screw caps on the top of the battery. It's perfectly natural for the electrolyte level to fall, and it should only be replaced with deionised or distilled water. If your battery doesn't have a level marker on the side (leisure batteries seldom do), only add enough water to cover the exposed plates before putting the battery on charge.

Leisure battery charging and discharging.

I've been asked several times if the 230-volt power supply unit in a caravan is a leisure battery charger or is it simply a 12-volt power supply, to which the answer is - both!

12-volt power supply or an intelligent charger

Older caravans often had a 'charger' that supplied a constant 12-volt output. Great for powering appliances but not so good for leisure battery charging. A separate charger would need to be used to charge the battery fully. Follow the supplied instructions on how to charge a leisure battery.

Newer caravans adopted a smart or intelligent charging system to deliver a higher initial charge before dropping back incrementally as the battery's needs were automatically monitored. The smart charger would also monitor the battery as appliances were used, keeping the battery in a fully charged state.

Your caravan's handbook should explain whether you have a 12-volt power supply or an intelligent charger.

Self-discharge.

The best leisure battery will slowly discharge, even when disconnected. At a temperature of 25°C, a lead/acid battery will self-discharge 9% per month, whereas AGM and gel batteries lose approximately 3%. It's worth monitoring your battery, even if you haven't used your caravan.

Leisure battery, solar charger.

Are you wondering how to charge a leisure battery with a solar charger? Solar panels, especially roof-mounted units, are used by thousands of caravanners to prolong battery life. I've been using a Truma 100w set-up for many years, and it is a fit-and-forget way to keep your leisure battery shipshape during trips, especially when using the shower, heating, TV, etc. I'll be conducting a test shortly to see if a solar panel can charge a lithium battery as effectively.

Different leisure battery types - lead/acid, AGM. gel, and lithium.

To date, my experience has been limited to lead/acid, although that is due to change shortly. I'm often asked about the pros and cons of lithium leisure vehicle batteries, so I'm testing one this year - in all temperatures and conditions - to evaluate a lithium leisure battery in real-world conditions. After all, lithium batteries can be a significant investment. Then, with the season-long test complete, the battery will be returned for analysis. I'd like to thank the kind folks at BBL Batteries for supplying an Avon Lithium battery and helping with the technical aspects of different battery types in this article.

#1 Wet lead-acid batteries.

Open lead-acid batteries are the least expensive, and as the name suggests, they consist of open battery cells. These batteries are popular because of their proven, straightforward technology. Sealed lead-acid batteries don't come with removable caps, so the electrolyte level doesn't need to be periodically checked. Because of this, it's considered maintenance-free.

#2 AGM Batteries.

Absorbed Glass Mat batteries feature glass mat separators saturated with an acid electrolyte between the battery's positive and negative plates. During charging, pressure valves allow oxygen produced on the positive plate to migrate to the negative plate and recombine with the hydrogen, producing water. AGM batteries have better shock and vibration protection than wet or gel batteries and are virtually maintenance-free. AGM batteries also have lower internal resistance, allowing greater starting power and charge acceptance. Recharge times are quicker than other types of deep-cycle batteries. AGM batteries can accept the highest charging current - up to 40% of the amp-hour capacity - compared to about 25% for the flooded type, or 30% for the gel.

#3 Gel Batteries.

The "gel" is a combination of sulphuric acid, fumed silica, pure water, and phosphoric acid. The gel is quite viscous and prevents leaks should the battery be inverted or the case is damaged. Charging does cause a small amount of hydrogen and oxygen to be generated at the plates, but the pressure inside the cells combines the gases to create water. This also keeps the battery from drying out due to charging. Gel batteries charge at a lower voltage than flooded or AGM batteries, requiring charging systems to be more carefully regulated to prevent high voltage overcharging.

#4 Lithium Batteries.

Battery technology is constantly evolving and developing. Although they've existed for a while, Lithium batteries are now becoming a popular choice in the consumer market.

Pro's & Cons for Lithium Batteries.

An online search will undoubtedly reveal hundreds of comments from leisure vehicle owners asking many questions about lithium technology. I've included key points below, so you'll know if lithium is the right choice.

Pros of Lithium batteries

#1 Weight

A well-known benefit of Lithium batteries is weight. 'The best batteries are the heaviest batteries' is a well-worn phrase, but that isn't true for lithium. Because they're lightweight - up to 50% lighter than lead acid - removing the battery from the leisure vehicle is no longer arduous.

#2 Life Cycle

As with all batteries, if you treat any battery well, it should have a long life. Lithium batteries can last longer - potentially up to twenty times longer - due to technology that offers more cycles per unit. If a standard lead acid battery can complete 500 cycles in its lifetime, a Lithium battery can complete 5000+ cycles at 50% depth of discharge (DoD). This is one of the reasons why lithium batteries have a higher purchase price. However, if you look at the total cost of ownership (TCO) of a lithium battery, it can be as much as 80% cheaper than a lead acid battery over its lifetime.

#3 Longer Runtime

You will often see lithium batteries being advertised as being 'twice the size' of a traditional lead/acid, i.e., a 100ah lithium being equivalent to a 200ah lead/acid. A lead/acid battery 'drops away' when used, reaching a 50% depth of discharge. In contrast, the voltage of a lithium battery stays very high until the battery is around 90% DoD but then drops away very quickly. The voltage effect of lithium allows your accessories and equipment to operate much longer whilst maintaining a high level of performance.

#4 Modern Features

Many Lithium batteries come with built-in BMS (Battery Management System) and Bluetooth. The Bluetooth function allows the user to view the battery's current, voltage, power, and state of charge from their mobile or tablet. The BMS ensures the Lithium cells are balanced for reliable performance and prevents the battery from fully discharging, which can cause damage.

#5 Efficiency & Durability

Lead acid batteries can be permanently damaged if discharged below 50% of their capacity. In contrast, a lithium battery can drop to a theoretical 100%, although a good BMS is likely to limit this to 90-95%. In addition, because of the composition, lithium doesn't sulphate when not in use.

Cons of Lithium batteries

However, there are points To consider before purchasing a lithium leisure battery.

#1 Chargers & Charging

Modern Lithium batteries have a BMS that allows them to be charged using most lead/acid chargers. However, always check the specifications of your charger or charging system when making your purchase, as some lead/acid chargers may only achieve 95% of the total charge of a lithium battery. If your vehicle has a charging system that goes beyond 15v, you need to use a DC-to-DC charger in-line to limit this.

#2 Temperature

While the operating window of a lithium battery is generally -20°c to +60°c, it is not advisable to charge a lithium battery at temperatures below 0°c. If you do so, you will not achieve a 100% full charge, and if you continue to recharge at below 0°c, you could damage your battery and permanently reduce its capacity.

Many Lithium batteries have their BMS set to block the ability to charge at temperatures below 0°c. Some batteries will also have an internally heated jacket that will use the charge source to raise the temperature to a level that the BMS will allow charging.

#3 High Current Draw

The other thing to consider, especially on caravans, is that Lithium leisure batteries are generally not designed to cope with high current draws, which can cause problems when using motor movers with four motor systems and larger AC inverters.

#4 Certification

You should also ensure that your lithium battery carries the required certifications, such as UN38.3, CE, UKCA, and RoHS. A good supplier will be able to confirm this.

How to get the most from your leisure battery.

1. Apply a thin layer of Vaseline or grease to the battery's terminals
2. Always use high-quality clamps
3. If spring-loaded clamps are used, ensure that the steel contact surfaces are rust-free.
4. Regularly check that the electrolyte level covers the lead plates on the battery (Open lead-acid batteries). If not, top up with deionised water as required. Always wear safety equipment when inspecting and maintaining the battery.
5. Check regularly to ensure the gas relief tube remains fitted securely and correctly.
6. Recharge the battery once it falls below 50%. Never allow a lead acid battery to run flat, as this can significantly reduce the lifespan.
7. Remember to care for your battery when your caravan or motorhome is unused. A trickle charger is a good idea in this situation.
8. Never leave a lead acid battery uncharged. A white deposit, caused by sulphation, will form on the plates, rendering the battery unusable.

Frequently asked battery questions

Q: Do I need a special charger for a leisure battery?

Common questions are 'Do I need a special charger for a leisure battery?' and 'what amperage should you charge a leisure battery at?' It is recommended that a battery has a charger with an output of around 10% of the battery's capacity. For example, a 100Ah battery will need at least a 10-amp charger. Any less could significantly reduce the capacity and the battery's overall serviceable life.

Q: How to test a leisure battery?

With all appliances turned off, your caravan's battery meter will give an indication of charge.

Q: How long does a leisure battery last?

With careful use, it's more than possible to enjoy a long weekend. This can be extended with a solar panel.

Q: Is a leisure battery ok if it has been flattened?

If your battery has dropped lower than 12 volts, its performance will be impaired at best.

Q: How to check the capacity of a leisure battery?

Battery capacity is measured in amp hours, displayed on the side of the battery.

Q: How to check the charge level of a leisure battery?

Using a multimeter, or your caravan's battery meter, a fully charged leisure battery should display 12.7 volts or more.

Q: What is a deep cycle leisure battery?

A deep cycle leisure battery is designed to produce steady power output over an extended period. Once the battery has discharged, recharging will complete a cycle.

Q: Do I connect leisure batteries in series or parallel?

Batteries should be connected in parallel if you're looking to double the available amp hour. Connecting in series will double the voltage, producing 24 volts from two 12-volt batteries.

What affects a battery's performance?

A few factors may affect a leisure battery's performance, including temperature, age, and the size of the battery.

#1 Temperature.

The colder the temperature, the poorer the battery's performance. The amp hour rating is based on a temperature of 25C, with each degree lower causing a 1% drop in performance. For example, a 110Ah battery operating at 15C temperature will perform as a 100Ah.

#2 Age.

All batteries are finite. A real difference can be made to their longevity by caring for and maintaining them regularly. It's uncommon for a lead/acid battery to last more than five years due to a decrease in performance over time.

#3 Consumption.

Frequent recharging (cycling) will cause the battery to degrade sooner.

#4 Size.

The more appliances you run, and the more power-hungry those appliances are, the bigger your leisure battery will need to be. For example, a motor mover will require a larger battery.

If you're wondering how low should I allow the voltage on a leisure battery to go to, 12.4-volts on a lead/acid unit.

Who can fit a leisure battery for me?

Several readers have asked who fits leisure batteries. Your local caravan dealer is an excellent place to start or contact the BBL Batteries team for your nearest retailer.