Batteries
Purpose
Drive Battery
Is the battery that's responsible for starting and running the engine as well as associated services such as ECU's, lights, fan, dashboard, stereo and so on. These batteries are designed to unload significant power to start the vehicle, then be immediately recharged by the alternator and kept at a high state of charge. These batteries will suffer if they are regularly discharged by more than 20%.
Leisure Battery
Is the battery responsible for running the rest of the vehicle, interior lights, fans, entertainment, fans for heaters, fridges, water pumps etc. These are deep cycle batteries which are designed to go from full to half charge regularly without damage.
Types
Float, Flooded, Wet or Liquid Lead Acid
A very common battery which is constructed of lead plates submerged in an acid solution. Batteries range from 40Ah right through to 140Ah depending on size and demand with an internal resistance of around 10-15%. You can discharge this type of battery to 50% without damaging it. The nominal voltage should be 13.5 and should be charged at 14.5.
Gel, AGM or Sealed
A battery that instead of using a liquid uses a Gel and this has the advantage of being maintenance free. Batteries range from 60Ah right through to 190Ah depending on size and demand with an internal resistance of around 2% and can be discharged to 80% without damaging it. The nominal voltage should be 13.4 and should be charged at 13.7.
Lithium
This is a minefield with many manufacturers producing '12V' batteries that are not suitable for various tasks, and its way beyond the scope of this article to cover this, but we will write a separate article specifically on Lithium batteries providing help and advice.