My virtual Caravan Site 

Caravan Battery
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What battery shall/should I buy?

The most common question asked and in some ways the most difficult as it will depend on five main factors.

A) do you have a mover?
B) does your van have an Alarm?
C) do you use your van off
Electric Hook Up?
D) will it physically fit?
E) what can you afford?
For many people the battery they will use will be the one stocked by the Dealer they bought the van from. Normally they will stock two sizes 85Ah or 110Ah and recommend the larger one if you have a mover. The make will vary but because most Dealers don't want a come back they will be of reasonable quality but not necessarily a make you will have heard of. One thing will be that it will physically fit the box in the caravan.

There are many manufacturers of batteries and many different qualities. Buying a Leisure Battery should mean that it is designed for the job.
Lucas, Numax , Elecsol and Banner are some of the brands available. There are specialist suppliers of batteries that will ship them to you via a courier. One of these recommended by many is Tanya Batteries I have not bought from them but they are worth a look.

When I looked to replace my battery recently after much research I chose a Banner Leisure Battery. They are manufactured in Austria and are designed for Leisure use having heavier lead plates etc. Many people on the forums recommended them to me and I decided on a 110Ah battery that suited my needs. I bought from Road Pro well known in the mobile leisure industry and was very happy with the service and price.


Banner Energy Bull 110Ah Battery
The K ratings are important. They give the capacity of the battery which is dependant on the rate the current  is taken from them.

So in my batteries case the stated capacity figures are K5 75Ah - K20 100Ah - K100 110Ah this means if discharged over 5 hours you get 75Ah where as discharged over 100 hours you get 110Ah. Hence it is very important when comparing battery capacity to compare the same discharge times.

What is a Leisure Battery?
Sometimes known as Deep Cycle Batteries or Marine Batteries, leisure batteries are specifically designed to provide a moderate supply of current over an extended period. They are normally used in Caravans, boats etc. to power lights, T.V's and other low power electrical devices, but can also be found in golf carts and motorized wheelchairs. Whilst the basic construction is similar to a car battery, they have thicker active battery plates and also thicker separators between the plates this reduces the loss of active material during discharge and recharging cycles and allows them to be discharged to a greater degree. Standard car batteries are designed to provide very high current for a short period and generally are not designed for deep discharges. To keep a battery healthy it should never be fully discharged and kept where possible fully charged.

Size required

The capacity/size of the leisure battery needed in a caravan is dependant on a number of factors. Is there a Motor Mover fitted, if so a higher capacity may be required as these take quite a high current and need a good capacity battery. Will you be using the caravan on sites without Electric Hook-Up? If so a higher capacity is required to give a longer period of power availability.
Will it physically fit into the battery compartment is another major consideration and is there enough room for the battery/mover cables to be fitted.***see below
In my case I chose a 110Ah battery as I have a Motor Mover and do sometimes have weekends away on Sites without EHU.
Approximate state of charge of a 12v battery
Charge Volts
or above

The voltages are measured with with no load on the battery and at least 6 hours after charging. The battery should be recharged when the capacity reaches 75% and to extend the life of the battery it should not be allowed to drop below 50% and never below 25%

Battery Charging

 Most modern caravans have two electrical systems, one for Mains Electricity 230V and one for the 12 volt side of things.

They are connected in that there is a Mains powered transformer which runs the 12v side and charges the Leisure Battery.

When no Mains is available the Battery takes over and runs the 12v appliances.

To call the system 12v is slightly misleading. A fully charged 12v battery in good condition will in fact give a reading of 12.7v and be only 25% charged when the voltage drops to 12v.

When the Mains power supply is on the voltage in the 12v system of the Caravan will in fact be 13.8v because this is the voltage used to keep the battery topped up. The devices, fans, lights, pumps, etc. in the van will run quite happily on this voltage.

A 12 volt battery requires a charging voltage of 14.4v for it to become fully charged. In most older Caravan systems the voltage does not rise above 13.8v, this is so that the battery does not overcharge and start 'gassing'. Hence, in a Caravan with this charging mechanism the maximum the battery can reach is about 80% of its full charge. This is why you see people recommending that now and again you should fully charge the battery using a separate 'intelligent' or 'smart' or sometimes called 'stage' charger. This type of charger monitors the battery during the charge process and changes the charging voltage accordingly to ensure a fully charged but not overcharged battery. Some modern Caravans come with this as standard and you don't need to separately charge the battery.

If a battery is allowed to run down and remain fairly discharged yet alone flat, it will deteriorate and quickly fail. To remain healthy a battery should be charged as soon after use as possible and never left flat.

Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.

Bulk Charge
The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.

Absorption Charge
The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.

Float Charge
The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging. The float voltage should be around 13.0 to 13.20 volts.

My Aldi smart, 3 stage, charger showing a fully charged battery on a float charge of 13 volts.
'Old' battery in Caravan 'New' battery in place
*** Physical size of a battery

The physical size of a battery is important as it has to fit into the battery box and leave room for the cables. My banner Battery (above right) has dimensions of
Width 354mm  Depth 175mm Height 190mm The depth 175mm is fairly normal and just fits in comfortably. The width 354mm is about the maximum that will fit. The height tends to be the crucial factor. My battery is a low profile battery at 190mm and leaves good room for the cables, I need this room as I have a Motor Mover fitted and the heavy duty cables with the normal battery leads are quite 'bulky' and stiff. It is the height of batteries that varies the most, and although I have good room above mine, the battery box slopes down at the back and restricts the maximum height you can fit. As can be seen my Avon Leisure battery is also a low profile one and leaves plenty of room.

On a previous van, with a taller battery, although the battery just fitted I had great trouble getting the connectors and cables to fit in so that I could close the door.
I almost bought a Numax Leisure Battery, this time, which had good reports and a good price, but, it was 242mm high and I wasn't sure if I could fit it in, with the cables, as it is 52mm taller than the Banner and Avon batteries, 2 inches in  old money!!
Back on charge it was measuring 12.17V approx 50% charge