Many electric fences are powered by a 12 volt battery for many quite viable reasons. They are portable and do not need a power source close by. They may also be connected to a solar panel for permanent energy removing the requirement of charging them every so often.

It is quite possible to use ANY type of 12 volt battery BUT – like everything – there are poorer and better options that may be utilised. All batteries store energy in a chemical form and converts this into electrical energy by utilising a process where chemicals interact with each other to complete the process to provide the electrical energy that may be used.

There are two principal types of 12 volt battery;-

A CAR battery or a
LEISURE / DEEP DRAWDOWN / DEEP CYCLE (three titles for the same product) battery.

Both supply 12 volts but they are quite different in their construction.

CAR BATTERY - as used in Electric Fencing..

A car battery is designed to give an instance jolt of big power to start an engine followed by an immediate recharge. They are constructed by a series of positive and negative plates (originally lead oxide but now a range of alloys are being used – Lithium, Cobalt etc.) immersed in an electrolyte solution - originally sulphuric acid (H2SO4) and distilled water but now a range of pastes and jells such as lithium hexafluorophosphate (LiPF6) and other organic solvents are employed.

The more plates that a cell contains, and therefore form a larger surface, the greater the cold start power (CCA) that the battery can deliver. The plates are thinner and perforated by a host of small holes to offer a larger surface for the chemical reaction to supply that surge of power required when starting a car, This surge comes at the cost of cyclic stability so the unit suffers when it is discharged below acceptable limits (as happens on an electric fence) and the re-charge cycles are reduced hence affecting the life of the battery. The larger the surface area of the plates including the holes - the faster the chemical reaction will occur supplying a stronger surge of energy.  These thin, perforated plates are affected by  a build-up of sulphates on the plates resulting in a reduced effectiveness so are less conducive to periodic recharging when a Car Battery stands for a length of time.

Early batteries had screw plugs which enabled them to be topped up with distilled water. Modern batteries are completely maintenance-free. Water does not need to be - and must not be topped up. 

Anatomy of a Battery

LEISURE, DEEP DRAW-DOWN or DEEP CYCLE BATTERY.

All three names refer to the same type of battery. Generally used in boats and caravans.

The basic construction of a Leisure Battery is essentially the same as the car battery except with a difference in the manner in which the plates are made. These plates are thicker and not perforated. The surface area available to carry out the chemical reaction to supply that surge is substantially less than a Car battery. This means that the battery is designed for a slower release of energy with a higher charge throughput – the continual charging and discharging process. Hence these batteries are also known as “Deep Draw-down batteries” These thicker plates release their energy slower because of their smaller surface area and rarely lose 'too many' electrons and will not suffer the same level of destruction via sulphate build-up. This means that a leisure battery can stand being discharged and recharged periodically. They will ultimately power your Electric Fence for a good deal longer than a car battery before needing replacing. It may be expected that a Leisure Battery will last substantially more recharging cycles than a car battery. 

Everyone likes a bargain, if you can get cheap car batteries from a source then there is nothing wrong with using them - simply be aware there are complications.

When should a 12 volt battery be recharged?

All energisers are essentially transformers and will convert the 12 volt input energy to 6000 volts output energy. If your battery loses 20% of its energy then your fence will lose 20% of its energy. Most energisers will continue to operate until about 9 volts when it will cut off. Battery Manufactures will recommend recharging at 11 volts. How long this will be depends on the capacity (measured in AmpHours) of the battery and the consumption of the energiser (measures in milliAmps). Divide the energiser consumption into the battery capacity will give you an approximate length of operation. An Energiser that consumes 180 milliAmps (a mid range energiser) connected to a 100 AmpHour capacity Leisure battery should last 550 hours - although there are other factors like animal or vegetation challenge, temperature, fence quality that will impact that.

These batteries are available from 12 Amp Hours to 250 Amp Hours. The cost of batteries is directly correlated to the increasing ampHour capacity. In most cases a 60 to 80 ampHour battery is adequate.

State of Charge
Charge 6v Battery 12v Battery
100% 6.37 12.73
90% 6.31 12.63
80% 6.25 12.5
70% 6.19 12.37
60% 6.12 12.24
50% 6.05 12.1
40% 5.98 11.96
30% 5.91 11.81
20% 5.83 11.66
10% 5.75 11.51

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4 comments

  • A very simple and concise explanation on the difference between the two types and why it is best to use a Deep Drawdown battery on my Electric Fence.

  • Thank you for the useful info. I have a 18V battery , can I use instead of the 12V?

  • Thanks for the information and the illustrations, very helpful thank you.

  • Very simple explanation of the difference. Easy to understand.

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