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Special Purpose and Off-Grid Batteries


Special purpose batteries could be better described as ...

Batteries used for Off-Grid housing and other special purposes  

A battery is made to carry out a specific role. If the type of battery is chosen well, it will perform well.

In each of the techologies, flooded, maintenance free (calcium), AGM or gel, the battery will be designed for a particular purpose.  
The purpose will be to start you vehicle, supply power for your motor home of stand-by for emergencies in a power outage to operate equipment such as burgler alarms, emergency exit signs or self opening doors - the list is very long.
If the battery is not chosen correctly, you will be disappointed with the length of time it has lasted and cost you money.

You don't have to be involved in the chemical technology, thats our job but you do need to appreciate that they do differ.

Off-Grid House banks

The sun dosn't always shine, the wind dosn't always blow so how do we smooth the supply. You cannot always draw power from the grid in times of poor or zero power producton. The answer is to harvest power from high production periods and store it for those down times. 

Storing power in batteries is a straight forward concept but determining the battery type is not so straight foraward. We have found many solar installation specailists are not necessarily electrochemical specialists or they may have only one battery option in there arsenal - they may not have the battery experience to advise you of your best option.

Battery Technology NZ Ltd, thats us, we are not involved in solar array installation but do have the electrochemical background, knowledge and experience to understand your battery requirements. Not all batteries are suited to solar or wind support and will not tolerate 'partial state of charge' (PSoC) conditions.

So what is PSoC. Partial state of charge. When a battery being cycled, it does not always reach full charge before it is being discharged once more. Therefore is operating in a partially discharged state. Once a lead acid battery is being discharged, it forms lead suphate, mainly on the negative plate. If that lead suphate is not disolved through the recharge process in a timely manner, it will form dendritic crystals (hard crystals) and not disolve. This condition reduces the capacity (AH) of the battery which gets worse as time goes by.

Using a carbon based negative plate negates the suphation problem and the battery retains a clean healthy condition over thousands of cycles. Solar power source is not consistant, clouds go by and the sun sets, and therefore the battery typically operates some times, as low as 50% depth of discharged (DoD) and cycles around that point.

The introduction of Lead carbon (PbC) some years ago now, is designed for just that purpose, negate sulphation and has revolutionised battery performance and longevity in solar, wind and automotive systems, and yes, we can help.


A battery used to start another engine will have thin porous plates to assist chemical reaction to act quickly, producing instant high current demands.


This battery has thicker dense plates to last many discharge and recharge cycles as used in a forklift application and multiple other applications including Off-Grid battery banks. Used all day and recharged all night or visa versa.

If the start battery is used in cyclic applications, its thin porus plates will distort from the heat of discharge and fail.


A battery in a floating application would be expected to retain a fully charged state, possibly for years waiting for the day it must respond to duty. This is a power backup system in case of power outages for the telecommunication or power supply industries and of course, your computer, alarms and others.

It is not possible to generalise accurately but a flooded battery may be good for starting, an AGM may be good for floating and a gel may be good for a cyclic life. And as always, their are variations and exceptions of these.

A couple of examples:

Now these applications are pretty standard but what about the battery to perform for say 3 days in a remote unattended location to power monitoring equipment . This battery may be subjected to altitude and diurnal temperature variations ranging from below freezing to maybe +30 degrees. The application is cyclic because after its duty it will be recharged ready for reuse. But when it comes to sizing the battery, the temperature will have an effect on deliverable amphour capacity. This effect is demonstrated below.

Temperature% of capacity
40 degree 102%
25 degrees 100%
0 degree 85%
- 15 degrees 65%


It doesn't matter which battery this particular scale relates to, the point is that each battery is affected by temperature and is a consideration.

I was approached by a group who where using an electric motor to power a small underwater swimming aid (like a torpedo) and could not get the performance out of the batteries they chose. Their choice was mathematically correct but they had not consider the environment in which it would be operating. ie, 5 degrees.
This low temperature reduced the capacity of the battery by 13% (according to the table above).
It fell short of their expectations.

The point I'd like to make here is that when you need a battery for a special purpose, a little investigation as to the environment it will endure and the performance needed is a must.
It would then be possible to narrow the search down and make the best selection.

There are also of course, batteries made for special purposes but unless you are the developer, the best battery will have been specified. Follow the manufacturers recommendation.




Model: Vertex Drycell V1220HD


Lighten up your race car!

Remove the heavy 20KG battery and replace it with the BatteryDirect 5.8KG Vertex Drycell.
The Vertex produces more power per pound than any battery on the market. It has the cranking power of wet cell batteries three times its size! This is due to the extremely low internal resistance which allows faster, more consistent starting. The Vertex does not have a cold cranking amp rating, but has been tested to crank engines with compression ratios as high as 13:1. The capacity of the Vertex is 20 AmpHours.
The Vertex Drycell is truly maintenance free and can withstand the rigors of high performance and racing environments.

The Vertex has an excellent storage life and recharges very quickly. Any 12 volt charger can be used to recharge the Vertex but a low amperage battery charger/maintainer, much like the charger/maintainer we sell is recommended to avoid overcharging the battery.

Click for battery chargers


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