There are commonly two power levels of battery that are used in caravans 85A & 110A.They should be designated as leisure batteries, normally sealed. Motor or vehicle batteries are not the same, they charge differently and should not be used.
There are three main categories when purchasing batteries
These are higher-powered batteries designed for more off-grid applications and running longer without being charged and hooked-up to site power
These are the common batteries mostly used, these are for normal usage and designed to be used while regularly hooked up to site power to charge and the battery capacity for motor mover etc.
These are for users that require a lower capacity battery to cover basic 12v operation of habitation equipment with short periods away from hook up and recharging. These are for small day campers or small van conversions.
Your battery should have a charge between 12.75v and 13.4v for a fully charged battery. A fully discharged battery has a voltage of 12volts(Twelve). So a battery with 12.5volts is deemed to have 50% power.A battery that has 12volts will still work the appliances but will seem to have dim lights or a slow water pump. Motor movers will drain an insufficiently charged battery very quickly. To know if your battery charger is working make sure you have mains power on, make sure your battery charger is switched on. If you have a voltage reading indicator then this should be showing 13.4v or in the green. If you switch your mains off and the battery indicator drops down to 12volts then switch on the charger again and observe the voltage indicator move higher to show 13.4volts this is a basic indicator of a working charger unit. Most new caravans will supply a 12v feed via to all 12v items even if the battery is flat. Be aware that your charger may be at risk of overheating or failing if you keep using a battery that is flat or not taking a charge. A leisure battery has thicker lead plates that hold the charge, leaving it to go flat will cause sulphate gas and cause the battery to suffer power loss. IF YOUR BATTERY IS VERY HOT OR HAS A STRONG GAS LIKE SMELL DISCONNECT FROM THE CARAVAN AND REMOVE IT, STANDING IT WELL AWAY FROM ANYTHING OR ANYONE AND ALLOW TO COOL. DO NOT USE IT. This battery will need to be replaced.
Leisure batteries require them to be trickle charged most of the time. Your built-in mains charger in your caravan or motorhome is designed to trickle charge at the optimum rate to keep your battery topped up.
If your caravan or motorhome is stored at your home then keeping it plugged into the mains with the charger on is sensible. However, to save money if you are not using it then a plug in timer can be set to charge a few hours a day. Just before you are going away I would recommend leaving the power and chargers on a full 24hrs.
If you are storing your motorhome or caravan a good solar panel installed will keep your batteries topped up and not go flat.
If you don't have a solar panel fitted and your leaving the caravan or motorhome ins storage for any extended period or over the winter then I suggest your remove the leisure battery altogether. Buy a specific leisure battery, keep it in your garage connect it and maintenance charge it. These leisure chargers trickle charge and keep your battery at its optimum level without overcharging.
If you are using your home power or a leisure charger in the garage do check the battery from time to time. In the caravan or motorhome turn your mains power off and take a reading from the meter level or readout. This will ensure that the battery is charging and not failing..