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;-

1/- CAR / INITIAL SURGE Two names for the same type of battery

or a

2/- LEISURE / DEEP DRAWDOWN / DEEP CYCLE three titles for the same type of battery.

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


A car battery is designed to give an instant surge of big power to start an engine followed by an immediate recharge. They are constructed by a series of positive and negative plates (originally primarily lead oxide (Pb3O4) (modern batteries utilise a range of alloys are being used – Lithium, Cobalt etc.) immersed in an electrolyte solution - originally sulphuric acid (H2SO4) and distilled water, (modern batteries now use a range of pastes and jells such as lithium hexafluorophosphate (LiPF6) and other organic solutions.) These electrolytes are absorbed into a fibreglass mat.

The more plates that a cell contains, and therefore form a larger surface, the greater the cold crank amps (CCA) that the battery can deliver. The plates are thinner and perforated by a host of small holes to offer the largest possible surface area for the chemical reaction to occur that supplies that surge of power required when starting a car, This surge comes at the cost of cyclic stability so the battery unit suffers when it is discharged below acceptable limits (as happens on an electric fence) and the re-charge cycles are reduced (as happens with an electric fence) - 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.  During discharge non-crystalline sulphate matter is left on the plates and during immediate charging this material is mostly transformed back to the starting compounds of lead, lead dioxide, and sulfuric acid. Batteries operating in a discharged state will see the non-crystalline sulphate matter harden into a crystalline form. Normal charging will no longer reverse this effect. Sad, but true. This is why sulphation is the #1 killer of lead acid batteries.

The Cold Crank Amp rating is NOT important for an electric fence as they draw minimal amounts of constant energy without the requirement for an immediate release of considerable energy.

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


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 of energy 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 limitations.

The Future, The development of electric cars and electricity storage is spurring the development of lighter, more efficient batteries. Whether it’s solid-state batteries, hydrogen fuel cells, redox flow, bio-electrochemical, sodium-based batteries, magnesium-based, aluminium-ion batteries or silicon anode technology, the development of the Solid State Battery, or a combination, is the most likely. These will be lighter, smaller and longer lasting than existing batteries. 

A solid-state battery utilises a solid electrolyte, This solid can be made of various materials, including ceramics, polymers, or sulphides. It has a higher energy density than a Lithium ion battery that uses a paste electrolyte solution. Then there is more space to put more active materials which increase chemical capacity in the battery.  A solid-state battery can increase energy density per unit area since only a small number of cells are needed. 

The anticipated advantages of solid-state technology are substantial. The lack of a liquid electrolyte makes these batteries less prone to leaks and the dangerous thermal runaway events. The solid electrolyte is also more resistant to dendrite formation, a phenomenon where lithium deposits grow through the electrolyte and create a short circuit, potentially leading to battery failure or fire.

Solid State Sodium batteries are made from material that is far more abundant than lithium (Salt is Sodium chloride NaCl) but production is proving difficult. Sodium sulfide (Na2S) is as active as lithium ion but safer, lighter and cheaper to produce and operates at a higher temperature.

The other future improvement is the development of Bipolar Batteries from the current Monopolar battery. In the Monopolar battery the energy is transmitted in a winding "S" fashion across the plates whilst the Bipolar with its straight metrics will move the needle further.

When any - or all, of these developments will filter down to a usable battery on an Electric Fence is anyone's guess.

When should a 12 volt battery be recharged?

All energisers are essentially transformers and will convert the 12 volt input energy to the 6000 odd volts energy that your fence runs on. 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 (measured 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 roughly 550 hours - although there are other factors like animal or vegetation challenge, temperature, fence quality that will impact that. (100 / 0.180 = 550)

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. Agrisellex does sell a range of Deep Drawdown batteries. 

The table reflects the available charge to run a 12 volt energiser based on the recommended recharge at 11 volts and not a percentage of the total available charge.

State of Charge
Charge 12v Battery
100% 12.73
90% 12.63
80% 12.5
70% 12.37
60% 12.24
50% 12.1
40% 11.96
30% 11.81
20% 11.66
10% 11.51

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  • Hi I need to stock proof circa 1000 metres of electric fence with associated post and batteries, can you please quote thanks

  • Concise and clear. A great help to my decision making when selecting a battery for my sheep net fencing. It’s a shame I can’t get this quality of info from a local Canadian supplier! I have to go across the pond for this type of quality information…so be it. Thank you!

  • 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.

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