There are two electrical systems in most modern caravans
 A) 240v Mains Electric.
This supplies power through a hook up lead to the refrigerator, three pin mains sockets,240v lighting (if fitted) a transformer (if fitted)Emerson heater (if fitted) and 240v space heater (if fitted)
 B) 12v Battery System
This supplies power from an on board battery to the water pump, 12v strip lights, toilet pump(if fitted) the gas side of the water heater and any blown air heating fan.

Why Are There Two Systems?
  The 240v mains system runs all house hold appliances such as T.V’s hairdryer’s etc.It also runs high wattage appliances such as fridges and kettles.
 The 12v system runs all low wattage items such as water pumps, striplights etc. A battery is used for the 12v system. If a power cut occurred you will still have lights and water.This is why it is important to check the operation of the battery.

How Is My Battery Charged?
 If you have a transformer on board and are plugged into the mains hook up the 240v from the mains goes through the transformer, is converted down to 12v’s, which is wired to the battery and keeps it charged up.

Do I Still Need A Battery?
  The answer is YES, the battery “levels” the voltage at 12v, the transformer on its own can give up to 17v, some of the electric's in the caravan are volt sensitive and could be damaged. Also, if there was a power cut you would have no lights.

How To Check Your Battery.
  This is important for the above reasons and is simple to do. If you use the mains all the time and you have a transformer you may not know if the battery is working independently.
  Disconnect the mains lead, the strip lights and water pump should continue to work.
If they don’t first check the main battery fuse which is situated somewhere near the battery, if that is ok the battery needs to be checked.
 If you have lost your 12v system it could mean your transformer has stopped working and the battery has gone flat due to normal use without charging.