This page gives information on the differences in specification between batteries used for starting a vehicle and the leisure/auxiliary/marine battery for running 12 volt appliances.
Jargon & Information about your starter battery, or your leisure battery.
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.
What does the 'CCA' rating mean?
The power the battery can deliver for a given time under certain conditions is usually referred to as its CCA (cold cranking amps). There are various different methods of measuring the CCA, but the most popular standard in the UK is the SAE (Society of Automobile Engineers) method.
Ampere-hour ratings (Ah)
The ampere-hour rating given to a battery (more relevant to leisure batteries than starter batteries these days) denotes the amount of energy that can be taken from the 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 ampere-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 ampere-hours is often abbreviated to amps (e.g. 85 amp leisure battery).
Tip!
Battery maintenance
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). NB: sealed for life batteries canot be topped-up.
Battery removal & re-fitting
When removing a battery disconnect the earth (-) terminal first and the live (+) last.
When re-fitting the battery connect the live (+) terminal fist and the earth (-) terminal last.
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