Eastpenn batteriesMany of the batteries in use in remote power systems have had their roots in traction batteries, however, battery technology has evolved significantly along with the growth of the telecom industry. The remote power industry has placed new and different demands on battery manufacturers to come up with cells capable of withstanding long periods of slow discharge at either very cold or very hot ambient temperatures.

We present the following information as a summary of the basic technologies available and their characteristics only. We invite you to contact us directly to discuss the number of battery options open to you depending upon your application and site characteristics.

Batteries in remote power systems provide for three things:

• Autonomy
The energy generated by the photovoltaic, wind or micro hydro system is stored in batteries in order to serve the loads over an extended period.

• Voltage Stabilization
Batteries prevent the voltage fluctuations emanating from the charge source from damaging the loads connected to the system.

• Large current demands
Renewable energy production is variable over time. Batteries meet large current demands whenever they are required.

The Basics

Batteries, or storage cells, are electrochemical devices. The principle components include one positive and one negative electrode comprised of numerous plates or tubes each made of dissimilar active material and an electrolyte all encased within a sealed or open container.

A chemical reaction takes place when a load is connected to the two electrodes, discharging the battery. The positive electrode absorbs negatively charged electrons from the load, while the negative electrode releases electrons to the positive plate. The electrolyte serves as the means by which the electricity, in the form of ions, moves. The reverse process occurs when the battery is charged.

When not connected to any load or charge current the battery's open voltage represents the potential energy between the electrodes that may be measured to determine the batteries state of charge. When fully charged this voltage will differ depending upon the type of battery - for example, each cell of a lead acid battery will have a VOC of about 2.10 VDC, while nickel-cadmium will show 1.25 VDC at 25 C.

Depth of Discharge (DOD) and State of Charge (SOC)

DOD is the ratio of amp hours removed from a battery versus its full capacity. For example 25 Ah are removed from a 100 Ah battery, thus it's depth of discharge is 25% and the battery is at a 75% state of charge.


One period of discharge and recharge is called one cycle. Battery performance may be measured by the expected number of cycles it may deliver at varying depths of discharge.

Selection of the type of Battery

Stationary lead (low or non-antimony) acid and nickel-cadmium are the types of batteries applicable to remote power systems. Within the lead acid category there are further classifications of vented and sealed batteries, also known as valve-regulated, and differing construction. Antimony is the alloy added to lead to increase its hardness. The high antimony content also reduces long discharge capability characteristic of remote power installation and increases the gases produced by the cells thus they should be avoided in remote power applications.

Nickel-Cadmium (ni-cad) batteries are generally 3 - 4 times the cost of lead acid cells thus their use is typically restricted to specialized situations of extreme hot or cold temperatures.

Battery Type
Cycle Life @ 80% DOD
Maximum DOD* (%)
Typical Capacity (Amp Hours)
- Flat Plate SLI
25 - 100
- Flat Plate Solar
80 -370
- Flat Plate Industrial
700 - 1500
- Tubular
700 - 2000
up to 5500
- Gelled Electrolyte
up to 6000

* DOD, Maximum recommended depth of discharge for this type of battery

Vented - Flat Plate

More than any other, the flat (1.6 mm) plate cell design is the most prevalent on the market in the form of SLI (starting, lighting and ignition) batteries. These are not suited for remote power applications. Similar in design are truck or golf cart batteries configured for solar applications. Though of similar construction to truck batteries they have much thicker (2.3 mm) low antimony plates capable of regular discharges of no more than ten or twenty percent. Industrial 2 VDC cells with plate thickness of 5 mm are well suited for these applications, however, care must be taken to ensure adequate ventilation is provided.

Vented - Tubular

Tubular type batteries are far superior to flat plate 2 V industrial battery design. In general the tubular design involves more electrolyte providing longer low current discharge, the construction is significantly stronger and the positive grid is either low or non-antimony (lead calcium) thus offering a longer service life. The low antimony tubular plate has been the battery of choice for telecommunications sites where maintenance and extreme cold temperature are non-issues.

Sealed (recombinant) Batteries

Sealed batteries recombine the oxygen that is normally produced on the positive plate with the hydrogen produced by the negative plate into water, thereby replacing the moisture in the battery. The oxygen is trapped in the cell by pressurized caps that lead to recombination.

It is generally recognized that an average annual wind speed of more than 18 km/h (5 m/s) is the required minimum for a stand alone wind-based system to be considered viable. For this reason the East and West coasts of North America, the far north and southern prairies offer the most promise for a primary wind power application. Outside of these areas wind turbines best complement solar systems or conventionally fueled generators to reduce fuel consumption in hybrid applications.

AGM type

The sealed AGM was developed during the 1980's to fulfill the growing need for a maintenance free battery for the telecommunications and UPS markets. These batteries use glass mat separators packed tightly between the flat plates to hold the electrolyte. Open, vented batteries produce excessive amounts of chemical energy producing heat, hydrogen and oxygen when charging whereas AGM batteries direct this oxygen gas to the negative plate where it is recombined into water.

batterieseast penn batteries

Under excessive or overcharging AGM cells tend to overheat and much of this heat is transferred to the cell terminals due to their means of construction. Heat dissipation is extremely important for this type of battery, particularly in warm climates. Too much charge current during the final stages of charging may result in the loss of acid via the cells release valve, particularly in cold weather. This acid cannot be replaced thus battery capacity is permanently reduced.

While some manufacturers claim other wise, AGM cells should always be installed flat, never vertically, to minimize stratification and the drying out of the cells prematurely.

Until recently AGM cells have been the preferred choice for cold weather climates, however, recent industry developments are demonstrating excellent results using the sealed gel battery.

Sealed Gel (Gelled Electrolyte)

Instead of the liquid electrolyte typically used in open cells, the electrolyte is mixed with silica to produce a gel. Sealed Gel batteries may be built with either flat or tubular plates and offer similar advantages with the added benefit of non-maintenance, non-spillable or leakable, superior deep cycle life, minimal gassing and stratification. Further, the nature of the gel cells' design facilitates their heat transfer when overcharged, thus reducing the potential for overheating.

The higher cost of the tubular variety of gel cells may be justified by their much higher cold weather current capacity, with higher cycling at lower depth of discharge than AGM.

Problems and Solutions


Heavier charged ions within a lead acid cell actually sink to the bottom of the cell, leaving discharged electrolyte or water (which may freeze) at the top. This results in two situations, oxidization of the top of the plates and faster corrosion at the bottom due to the higher acid concentration there. An equalization charge, as described below, will eliminate stratification.


Concentrations of 4% hydrogen are explosive, and recommended maximum concentrations of 2% are required for battery storage areas. Both open and sealed batteries require ventilation. Gel cells will produce higher amounts of gassing during their early service tapering off as the battery develops internal pathways for the internal movement of gases. Each amp to total overcharge will produce 0.00045 m3 of hydrogen per hour per battery cell in series. The maximum hydrogen produced by a power system is therefore: 0.00045 x # cells in series x max generator output current.

Matrix offers glazed solar collectors with PV direct DC fans that are designed to provide the required minimum ventilation and increase the ambient temperature thereby increasing battery autonomy. Contact us to review your ventilation requirements based upon the battery type, enclosure area, voltage and charge current.


Sulfation is the inevitable depositing of lead sulfate crystals on the plates within a cell that permanently reduces the capacity of the battery. Sulfation occurs as the battery is discharged. Very deep discharging of the batteries can cause the sulfate to expand the negative lead plates separating the lead from the grid or shorting it, permanently damage the cell. Batteries, which remain partially, discharged for extended periods of time develop "memory" of the reduced state of charge.

Sulfation is avoided by ensuring adequate battery capacity is installed initially, and avoiding extended periods of deep (>20%) discharge. The lead sulfate may be partially removed from cells via a controlled equalization charge whereby high (2.35 - 2.4 VPC) voltage is applied to the battery. Equalization charges are required after extended periods of deep discharge; if any cell has a variation of more than 0.05 V from the battery voltage; when temperature corrected specific gravity is 0.010 below the full charge value; once a year.



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