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Disclaimer. The information provided on this Web site is accurate to the best of our knowledge and is intended for guidance only. We accept no responsibility or liability for incorrect installations of any kind. If in doubt contact a qualified tradesman. Nor do we accept responsibility for information provided by third party Web sites linked from this site.
Leisure batteries
What's the difference between an engine starter battery and a leisure battery?
A leisure
battery is designed to deliver a lesser current over longer periods which is often
referred to as 'Cycling', or 'Deep cycling'. Leisure batteries are constructed differently
to starter batteries to withstand the many cycles of discharging and recharging.
It used to be inadvisable to use a leisure battery for starting purposes, but many
leisure batteries are now 'Dual purpose'. A starter/engine battery is designed to
give a quick surge of maximum power when you turn the ignition key and is not suitable
for 'Cycling' purposes.
There are 3 main types of leisure battery:
- “Flooded” or “Wet cell” leisure batteries - the battery is filled with liquid sulphuric acid (electrolyte) in the conventional way and periodic maintenance (topping up with de-ionised water) may be required.
- “AGM” (Absorbed Glass Mat) leisure batteries - the battery is filled with acid, but the liquid is totally absorbed making AGM batteries non-spill and so that they can be fitted in any orientation, i.e. on their side or at an angle.
- “GEL” leisure batteries - the battery is filled with an electrolyte gel thus making
them non-spill and GEL batteries can also be fitted in any orientation.
GEL and AGM batteries will provide more cycles (battery discharging and recharging) than conventional wet cell batteries and have deeper cycle parameters, but these advantages must be weighed up against the initial cost.
Never leave either a starter battery or a leisure battery in a discharged (flat)
condition as this will cause the battery plates to 'Sulphate' rendering the battery
useless and also invalidate any warranty. Lead-acid batteries must be left in fully
charged condition, ideally disconnected from the vehicle, and when left idle for
long periods a top-up charge should be performed periodically (the use of a fully
automatic battery charger is recommended). These rules apply to all types of lead-acid
batteries. Most modern lead-acid batteries require very little, or no topping up.
However, if on inspection (remove all filler caps), the electrolyte level has dropped
beyond the top of the battery plates top-up with de-ionised water to a level of about
1/4" above the battery plates in each cell (12 volt batteries have 6 individual cells).
Sealed for life, AGM and GEL batteries cannot be topped-up.
Amp hours explained.
The Amp hour rating denotes the amount of energy that can be taken from a battery
before the terminal voltage falls below 10.8 volts. This test is usually carried
out over a 20 hour period (20 hour rate). Thus a 50 Amp hour battery can be discharged
at 2.5 amps for 20 hours before the voltage drops below 10.8 volts (i.e. 20 x 2.5
= 50). With leisure batteries Amp hours is often abbreviated to amps (e.g. 85 amp
leisure battery).
How much 12 volt power (Amp hours) do I need from my leisure battery?
The simplest method of working your power consumption is as follows:
Watts divided by Volts = current in Amps. Thus on a 12 volt electrical system a 120w pump will take 10amps (i.e. 120 watts/12 volts = 10 amps). In theory, using the above equation, you might think that an 80 amp leisure battery would be adequate to run the pump for 8 hours, but in practise by the pump will fail to run properly as the battery becomes completely discharged so a safety margin of around 25% should be applied with regards to the battery Amp hours required. See the equation below:
i.e 10 amp pump to run for 8 hours = 80 amps + 25% safety margin (20Ah) = leisure battery of at least 100 Amp hours is required to run the pump efficiently.
It is also possible to do the equation the other way round by multiplying the volts by the amount of amps, i.e 12 volts x 10 amps = 120 watts.
Ok, let's show off. Here's another way 120 watts divided by 10 amps = 12 volts.
Get it now?