It is all about POWER (well, battery power)
Aside from enabling you to maintain your batteries in a way which will prolong its life and keep your costs down, being able to recognise the signs of potential damage in a battery is essential for safety.
The leisure battery
A leisure battery is the power source for the 12V appliances and equipment in a narrow boat. These batteries are designed to provide a steady level of power over a prolonged period of time and are used by the lights, T.V, kettle, oven and similar appliances in some outfits. Basically, they are the part that makes your vessel into comfortable, habitable accommodation.
Is a leisure battery just a different name for a car battery?
No, a leisure battery and a car battery are two very different power sources. It may be possible to use each of the batteries in the other’s place in the short term, but it is not advisable due to the different ways in which they produce energy.
A car battery is designed to provide a burst of energy to start the engine when required, whereas a leisure battery will release a lower level of energy over a prolonged period of time in order to power appliances.
Due to the difference in intended purposes, leisure batteries and car batteries are not constructed in the same way. A car battery has thinner plates and different separators, which mean that it is not as well-equipped to deal with a prolonged period of use for a lower level of energy, and vice versa for leisure batteries. There is a type of battery which can perform well at both functions, an AGM battery, but this is not commonly used.
Types of leisure battery
Most leisure batteries are lead-acid batteries, although we will provide information on some alternatives later in the article. Within the category of lead-acid battery, there are a few different types available:
- Standard starter batteries – also known as calcium or cranking batteries
- Standard leisure batteries – also known as auxiliary or deep-cycling batteries
- Semi traction and traction batteries – also known as deep-cycling batteries
As well as these lead-acid batteries, there are a few alternatives which may be used as leisure batteries in certain circumstances.
- Gel batteries – These are used in vehicles such as jet skis and quad bikes, which have a higher than average risk of crashing. The use of gel inside the battery removes the risk of damage from being tipped over and, therefore, the risk of injury from leaking corrosive acid.
- AGM batteries – We mentioned these briefly in the section about car batteries v leisure batteries. AGM, or Absorbent Glass Mat batteries comprises of lead plates and compressed glass fibre in each cell. Combined with specific manufacturing processes, this makes the battery capable of a much longer lifespan than a lead-acid one. However, it is also more expensive to produce. As well as being able to withstand a greater number of charging cycles, AGM batteries have the advantage of being functional as both starter and leisure batteries.
- Maintenance-free batteries – While conventional batteries have removable caps to allow the acid levels to be checked and topped up with deionised water, some manufacturers are now producing what is described as a maintenance-free battery. This is a sealed unit which cannot be topped up, built due to the fact that batteries which are not charged in excess of 14.6V rarely need this done anyway. If 14.8V or more is used, it is important to regularly check the electrolyte level of a battery and replenish as required.
Why should I use a leisure battery?
You will need a leisure battery in order for most of the 12V appliances in your narrow boat to function but, even if it wasn’t essential, there is a very good reason for choosing to use a leisure battery rather than powering the devices directly from a mains charger or similar. The secondary function of a leisure battery, aside from powering appliances, is to correct any irregularities in the power supply, keeping you and your appliances safe.
Lead-acid battery safe handling
Due to the flammable nature of batteries and the corrosive properties of the acid within, proper safety measures must be followed when handling batteries.
- Ensure the battery is properly mounted and the gas escape vent correctly fitted at all times
- Safety clothing and eye equipment must always be worn when inspecting a battery
- High quality clamps should always be used to connect a battery to prevent any sparks from occurring and causing fire. Crocodile clips are not suitable for permanent connections
Getting the most from your leisure battery
- Apply a thin layer of Vaseline or grease to the battery’s terminals
- Always use high quality clamps
- If spring-loaded clamps are used, ensure that their steel contact surfaces do not rust
- Regularly check that the electrolyte level covers the lead plates on the battery. If not, top up with deionised water as required. Always wear full safety equipment when inspecting and maintaining the battery
- Check regularly to make sure the gas relief tube remains fitted securely and correctly
- Recharge the battery once it falls below 50% power. Never allow a battery to completely run flat as this can greatly reduce the lifespan
- Remember to care for your battery when your caravan or motorhome is to be unused for a period of time. A trickle charger is a good idea in this situation
- Never leave the battery uncharged. A white deposit, caused by sulphation, will form on the plates, rendering the battery unusable
- Remember that a battery needs a charger with an output of at least 10% of the battery’s capacity. For example, a 90Ah battery will need at least a 9 amp charger. Any less will significantly reduce the capacity
Checking the battery’s charge level
While your boat may have a light or display to show the leisure battery’s charge level, these may not be particularly accurate. It is advisable to invest in a hand-held metre, which can be used to easily obtain an accurate indication of the charge level. The table below can be used as a guideline when carrying out the checks.
| Meter Reading | Approximate Charge Level |
| 12.7V or above | 100% |
| 12.5V | 75% |
| 12.4V | 50% |
| 12.2V | 25% |
| 12V or lower | Discharged |
Prior to using the meter to check the battery’s charge, the following steps should be followed:
- Switch off all electrical appliances, including alarms, fridges and clocks that run off the battery. Failure to do so will result in an inaccurate reading
- Always remove the negative terminal first when disconnecting a battery
- Never smoke near a battery
- Do not use a charger on the battery or drive your motorhome for four hours before testing, as a recently used battery will give a higher reading
An alternative method of checking the charge level of a battery is using a hydrometer to measure the electrolytes in the cells. The reading should be between 1.1 (discharged) and 1.28 (fully charged).
To determine how long the battery can go between charges, check the capacity, which is normally measured in amp hours (Ah). An 110Ah battery will provide considerably more power between charges than a 65Ah one, for example, but will also take longer to recharge.
Always have a window open to allow gases to escape while the battery is charging.
Some users prefer to use a continuous charging system to keep the leisure battery functioning. While this may be perfectly fine, it is advisable to check with the manufacturer before continuously charging any battery.
What affects a battery’s performance?
There are quite a few factors which may affect the performance of a leisure battery, including temperature, age and the size of the battery.
- Temperature – The colder the temperature, the poorer the performance of the battery. The amp hours rating which is stated is based on a temperature of 25C, with each degree lower causing a 1% drop in performance. For example, an 110Ah battery operating in 15C temperature will actually perform as a 100Ah.
- Age – Most batteries will not last more than around five years due to a decrease in performance over time
- Consumption – If a high number of appliances are run from a battery, it will discharge quicker and therefore need to be recharged more often. This frequent recharging will cause the battery to degrade sooner.
- Size – The more appliances you need to 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 large battery. You should also consider the time of year you tend to travel, due to the reduction in performance caused by cold weather.
- Discharge rate – The Ah rating provided by the manufacturers of batteries normally assumes a discharge time of 20 hours. The capacity will normally be provided at two or three different levels, such as 95Ah at a 20 hour rate, 80Ah at a 5 hour rate and 105Ah at a 100 hour rate.
While all of these will influence the performance of the battery, it is important to remember that there are countless other factors at play. It is best to assume you will need to recharge your leisure battery sooner than calculations may suggest.
Hope you are enjoying this seasons cruising, stay safe and if you are passing Venetian Marina, please call in for a brew, the kettle is always on.