Charging A Leisure Battery From Flat (Some Great Tips)

A conventional leisure battery will give a cycling life of between 200 – 300 deep discharges. A Gel battery between 400 – 500 cycles and an AGM (absorbent glass mat) battery 600 – 800 cycles.

Batteries fail because of lead sulphation of the plates. Capacity loss is quicker with leisure batteries. The deeper that you discharge the battery and the faster lead sulphation will build up.

The problem with discharging a leisure battery too much is when you try to recharge not all the sulphation converts to lead. And this will cause a loss of capacity and the battery’s capability in holding a charge.

To completely discharge a battery could make this process irreversible, and a replacement battery will be necessary.  The gel and AGM style battery can withstand this process a little better. But in any case, avoid discharging a lead-acid battery below 50% capacity before you recharge it.

Charging A Leisure Battery

Although they look similar to a car battery, you shouldn’t confuse the two. They design your leisure battery to give off lower currents for longer periods of time and then recharge slowly.

A car battery, on the hand, needs to provide a high current powerful enough to start a car and for the alternator to keep it topped up.

To get the best results from your leisure battery charge it slowly over one to two days. This is far better than a shorter, faster charge. If you have a ‘smart charger’ or fully automated leisure battery charger it can stay connected to your battery causing no damage. 

The fully automated portable charger is the more expensive option, but buying a cheaper one can be a false economy. With a cheap charger, you need to be present to switch it off, when it reaches the full charge. If you forget and leave it too long overcharging your battery, it will cause serious damage.

Overcharging creates too much heat and eventually will buckle the plates and ruin their active material. The water will evaporate. The manufacturers seal the newer batteries and you can’t replace the lost water, reducing the life of the battery.

Before Charging A Leisure Battery

Before proceeding to charge your battery unhook it from everything. Still being hooked up can interfere with the process.

How long you charge your battery will depend on the discharge level. In the early stage, the battery will charge more quickly, but as it gets nearer to full charge, the process will slow down.

If you have allowed your battery to go totally flat, then it will have difficulty holding a charge. It could well take a few hours before you see any progress if you see any at all.

Some leisure batteries never recover from being allowed to go flat.

Checking A Leisure Battery Charge Level

Some caravans have a display that shows the level of your battery. But they aren’t accurate enough. So invest in a handheld metre, which can give accurate readings.

Before using the meter take a few precautionary steps:

  • Turn off all electrical appliances. This includes fridges and clocks running on the battery and any alarms you have rigged.
  • Unhook the battery by the negative terminal first.
  • Do not smoke or have any naked flame near the battery.
  • Make sure you haven’t used a charger on the battery within four hours of testing. You will not get an accurate reading.

You should expect readings similar to these:

  • 12.7V or above equals 100% charge
  • 12.5V                equals   75% charge
  • 12.4V                equals   50% charge
  • 12.2V                equals   25% charge
  • 12V                   Discharged  


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