Around 600 AD the Greek philosopher Thales from Milete discovered that when amber is rubbed against cloth, lightweight objects will stick to it. The friction had generated static electricity. The amber stone is called electron in Greek. Hence the name electricity. For the next 2400 years scientific research would focus on static electricity.

It was not until 1797 that Alessandro Volta created his famous Pile and entered the field of electrodynamics. From then theoretical interest in static electricity was lost and the 19th century would bring us a multitude of practical applications of electricity instead. To read more please expand the headers below.

Primary Cell

In 1786 biologist Luigi Galvani dissected a frog, every time Galvani’s steel scalpel touched a brass hook that was holding the frog’s leg in place, the leg would twitch. Galvani believed that this energy came from within the animal and called it ‘animal electricity’.

Galvani’s friend and associate Alessandro Volta disagreed. He was convinced that the electricity was generated by the two dissimilar metals in a moist medium. Experiments confirmed this and in 1797 Volta built the first real battery, the Voltaic Pile. The pile consisted of 49 pairs of alternating copper and zinc discs, which were separated by cloth, soaked in brine. When both ends were connected to a conductor a current would run.

In a voltaic pile, electricity is generated by chemical reaction and, once exhausted, the pile cannot be recharged. This is called a primary cell.

The Secondary Cell

In a voltaic pile electricity is generated by chemical reaction and, once exhausted, the pile cannot be recharged. This is called a primary cell.

In 1803 The German physicist Johann Wilhelm Ritter built a voltaic pile in reverse. The Ritter Pile consisted of copper discs only, also here separated by layers of substance or cardboard soaked in a saline solution. The column of Ritter could store electric energy, but not produce it. That is what we call a secondary cell, storage battery or accumulator. The electricity necessary to charge the Ritter pile, could only be obtained from a primary power source such as a voltaic pile. That made Ritter’s discovery interesting, but of little practical use.

1854 brought an important development – the German doctor and scientist Joseph Sinsteden placed two lead plates in a container with dilute sulphuric acid. The sulfuric acid reacted with the surface of the plates and formed a layer of lead sulphate. Sinsteden connected the plates to a primary power source and saw a layer of lead oxide forming on one plate and spongy lead on the other. After this charging the battery could be discharged again with a current of no less than 2V, much more than ever was realized by Sinsteden’s predecessors Volta and Ritter. During the discharge lead sulphate was formed on both plates just like the first time, so the process could start again. The lead acid battery was born!

The Planté Plate

In Europe Emile Alphonse Fauré made a lead paste consisting of lead oxide, sulphuric acid and water and applied it to lead plates, which after drying were then covered with lead sulphate. One single charge gave the Fauré plate a capacity many times that of a Planté plate.

Unfortunately, the adhesion of the active mass on the smooth plate surface was not very durable and after a few cycles the battery became unusable. The solution came at the same time from two different sides, John Scudamore Sellon and Ernest Volckmar produced both a perforated plate of lead with antimony, in which the lead paste of Fauré held much better. This is the same pasted grid plate which is still used in all flat plate batteries.

The new technologies – in particular the construction of the plates – were protected by a large number of complex patents. For this reason, many producers were looking for a replacement for lead oxide as a starting material. Around 1889 lead chloride was used by Clement Payen in America and by Francois Laurent Cely in England. After a few years, this process was aborted, but by that time they had grown into two of the largest battery manufacturers in the world: in America the Electrical Storage Battery Company and in England the Chloride Electrical Storage Syndicate, now known as the Chloride Group.

The Tubular Plate

In the Electrical world, 1890, Volume 16, a Mr S Currie is reported to have designed a tubular positive plate. The plate derives its strength from tubes, filled with active mass in which a lead spine serves as a conductor.

In this design mechanical strength and electrical conductivity are separated, in contrast to the grid plate which has to do both: support the active mass and conduct electricity to the terminals. A positive tubular plate consists of a number of spines, connected to a top bar like a fork.

Tubular batteries are very popular in Europe and Japan because of the excellent performance in stationary and traction applications. In English they are referred to as Ironclad batteries, and in German Panzerplatte (abbreviated Pz). Tubular plates can have 19 spines (DIN) or 14 spines (Brittish Standard).

Historical Context

With the development of the secondary battery the need arose for a better power source than a primary battery. This development had already been started by Michael Faraday with his discovery of magnetic induction.

In 1866, Werner von Siemens and Charles Wheatstone presented simultaneously a practical design for a Dynamo.

Zénobe Gramme invented in 1871 the Gramme Dynamo, which was the first to generate electricity on a commercial scale. Gramme discovered by chance that when two Gramme-dynamo’s were connetcted in parrallel, one dynamo acted as an engine, electrically powered by the other. The Gramme machine successfully developed into the first, industrial electric motor.

And so it all came together. The Dynamo could generate electricity, the secondary battery could store it and the electric motor could convert electrical energy into mechanical drive. The development and manufacture of secondary batteries went into overdrive. In 1890 for example – due to the unreliability of the combustion engine – nine out of ten cars were electrically powered.

Lead Antimony Batteries

The basic principle of the conventional battery is a grid plate casted from an alloy of lead and antimony, sometimes up to 12% or more. It is basically the same battery with pasted plates invented by Volckmar and Sellon 120 years ago. The antimony strengthens the soft lead, improves adhesion of active mass and protects against corrosion. Often additional components such as selenium and arsenic are added in order to further improve the properties.

At the end of charge the antimony can produce a very poisonous gas called Stibine or antimony hydride (SbH3). It has the distinctive smell of rotten eggs. Stibine is thermally not very stable: it dissolves slowly at room temperature. The decomposition products are hydrogen and metallic antimony. The latter will be deposited on the negative plate. As a result, the gas voltage at the negative plate will be reduced with sometimes 200mV so the battery will produce more gases and thus consume more water. At the same time the rate of self-discharge will increase.

As more antimony is deposited on the negative plate more Stibine will be produced during charging. More Stibine means more deposit on the negative plate, and this is why a high antimony battery will suffer from higher water consumption and self-discharge as it gets older.

Low Antimony Batteries

To reduce water consumption and self-discharge, the antimony content of the grid is reduced from 12% to 1-3%. These low-antimony batteries are sometimes called maintenance-free to or DIN43539/2 or EN50342-1. However, the standard EN50342-1 refers to a low water loss battery – when the water consumption is less than 4g/Ah Ce. Low Maintenance battery is therefore the better term, avoiding confusion with sealed maintenance free batteries (MF and VRLA).

Typical characteristics of the lead-antimony battery are:

Robust, proven technology that with proper maintenance provides a long service life.

Can be produced dry charged, for less transport weight, no safety issues and no self discharge when vacuum-packed, a dry charged battery can be stored several years.

Limited shelf life of three months once the battery is filled.

In the trade (low) lead antimony batteries are referred to as PbSb/SbSb, or simply PbSb which means that both the positive and the negative plate type lead-antimony. Pb stands for lead (Latin: plumbum) and SB for antimony (Latin: Stibium)

Calcium Batteries

Around 1970 manufacturers started to replace the antimony with calcium in starter batteries. Calcium in both the positive and the negative plates brings many advantages:

Low water consumption (< 1 g/Ah Ce) that is so low that the original quantity of electrolyte is sufficient to last the entire design life. Many manufacturers enhance this feature by omitting the filler caps and leave only a charge indicator. The term sealed maintenance-free (in short MF or SMF) can lead to confusion with Gel or AGM batteries. The electrolyte is in these type of batteries, however, not immobilized. When (over)charged hydrogen will escape like in any flooded battery.

Long shelf life because of the extremely low rate of self-discharge. A fully charged calcium battery can be stored for over a year before it reaches 50% state of charge (SOC) – sufficient to start delivering its cranking power.

Low internal resistance. This allows the calcium battery to deliver its cranking power very fast. It also makes the battery accept high charging currents, taking less time to recharge. This low internal resistance also has a downside: deep discharge may cause a vehement chemical reaction at the positive plate, causing loss of active mass and seriously shortening cycle life.

The lead calcium alloy is relatively soft. This property makes it possible for battery plates to be cut or punched from a strip, called expanded metal and punched plate technology respectively Lead calcium batteries cannot be dry charged.. In comparative charts and tables is the indication to the OJ CA series/OJ CA series or CA/approx In the trade these batteries are referred to as PbCa/PbCa or Ca/CA – Ca for Calcium.

Hybrid Batteries

In hybrid batteries we see a combination of the cyclic performance of the lead-antimony batteries and the low self-discharge of its calcium counterpart:

  • A positive plate of low antimony alloy for better resistance to deep discharge.
  • A negative plate of calcium alloy to improve shelf life (approx 6 months).
  • The hybrid construction proves very successful for commercial and dual purpose batteries.
  • Hybrid batteries cannot be produced dry charged.
  • In the trade these batteries are referred to as PbSb/SbCa.


Let’s look once more at the charging process. During the discharge the active mass on the plates has turned into lead sulphate. When charging the lead sulphate of the positive plate turned into lead dioxide whilst the lead sulphate on the negative plate turns into spongy lead. At the end of charge oxygen is released at the positive plate and hydrogen at the negative plate. When both gases can rise to the surface and leave the electrolyte, there will be water loss and the battery will need to be refilled with water.

Due to the difference in charge acceptance between the positive and negative plate gas will be released at the positive plate slightly earlier than at the negative action. By the time that oxygen is released on the positive plate already a fair amount of spongy lead has been formed on the negative plate. So if we could bring about that the oxygen does not rise to the surface, but instead travel to the negative plate, it will react with this spongy lead and form lead oxide. Subsequently the lead oxide will react with the electrolyte and turn into lead sulphate.

Lead oxide turning into lead sulphate is, as we know, the result of discharge. So we may conclude that by bringing the oxygen from the positive plate into contact with the negative plate, just before the latter reaches its gas voltage, a self-discharge will occur that is equivalent to the charge. This means no gas voltage – and therefore no water loss. For whom all this is too much, it should suffice to say that when oxygen can reach the negative plate it will ultimately recombinie into water – hence the name recombinant battery.

Recombinant batteries need for proper functioning some overpressure and are therefore sealed. A self-closing safety valve opens when the pressure exceeds preset level (> 0.18 bar) and will close as soon as the balance is restored (< 0.15 bar). This is why these batteries are often referred to as VRLA (Valve Regulated Lead Acid), the gas that is released in the case of overpressure will mainly consist of oxygen, but it contains some hydrogen. Because of the sealed construction and the pressure within, this water loss cannot be replaced and constitutes therefore an irreversible shortening of service life.

The most important features of a VRLA battery are:

Totally maintenance free.

Low gas emission under normal conditions, in a ventilated surrounding never exceeding the critical concentration of 4% which makes oxyhydrogen explosive.

No free acid in the event of damage.

Can be side-mounted.

VRLA vs AGM & Gel

Oddly enough, recombinant batteries are seldom referred to as such, but with the term VRLA (Valve Regulated Lead Acid) or SLA (Sealed Lead Acid). These terms refer to the safety valve and the sealed lid. Both elements are important of course but only so because they allow the recombination process to take place. The full name of a VRLA battery should be: Valve Regulated Recombinant Lead Acid Battery.

To produce a recombinant battery, a more or less solid electrolyte is needed through which the oxygen can travel to the negative plate. In time two techniques have been developed to immobilize the electrolyte: Gel and AGM. Both of these techniques serve the same purpose, namely a maintenance-free, safe and sustainable energy source. Both types have the sealed construction and the self-closing pressure valve in common. The only, but not insignificant difference lies in the electrolyte and the separators.

Because gel batteries are on the market for over 50 years, gel has become synonymous with the recombinant battery, and the term is often used when the battery in question is of the AGM type, which were developed twenty years later. This can be very disturbing, since AGM and gel batteries have very different charging parameters.

Gel Batteries

The development of a battery that would not spill electrolyte when damaged or falling over began shortly before the second world war in Germany. In 1957 Otto Jache filed on behalf of the battery factory Sonnenschein, the patent for an immobilized electrolyte by the addition of fumed silica, which will thicken the electrolyte into a gelled substance, much like petrol jelly.

Gel batteries are produced with flat plates as well as tubular plates. Flat plates have microporous PVC separators that provide good protection against loss of active material, albeit increasing internal resistance. Addition of phosphoric acid in the electrolyte increases the cyclical ability, but at the expense of an initial loss of capacity of around 15%, which only will be restored after about 20 cycles respectively a year of float service.

Deep cycle?

To many a gel battery is automatically seen as a deep cycle battery, suitable for deep discharge applications. That’s not necessarily the case. Just as with the flooded lead-acid batteries, the deep cycle performance is determined by the construction of the plates, not in any way by the electrolyte. The well-known Sonnenschein product range, for example, reflects the same subdivision we see in other battery technologies:

  • Dryfit Start (for Starting, Light and Ignition)
  • Dryfit Sportline ( Dual Purpose for Marine and R/V)
  • GF-Y (A500) (for Deep Cycle applications)
  • A200 –A400 (for UPS and other stationary applications)

AGM Batteries

In 1972 researchers of the American Gates Rubber Company developed a safe recombinant battery for the US Air Force, with the emphasis on power-to-weight ratio. This was accomplished by positive and negative plates of a calcium alloy, separated by microporous glass fiber mats, in which the electrolyte is absorbed by capillary action. The technique is called, therefore, Absorbed Glass Matt or AGM.

Microporous glass mat separators consist of thin, hollow tubes of unequal length. These fiber mats are only for about 95% saturated with electrolyte, the rest is used for the oxygen migration to the negative plate. This technique is called Starved Electrolyte. To compensate for the small quantity of absorbed electrolyte a Specific Gravity (SG) of 1.30 is used. The principle of starved electrolyte has also a positive effect on the cycle life of the AGM battery. When deeply discharged, the small quantity of electrolyte will be exhausted before permanent damage is done.

Deep discharge?

Just as with Gel batteries, many believe any AGM battery to be a deep cycle battery, suitable for deep discharge applications. That’s not necessarily the case. Just as with flooded batteries, the deep cycle performance of a battery is determined by the construction of the plates, not in any way by the electrolyte. AGM batteries are very popular for use in stationary applications such as emergency power supply, telecommunications etc. By using thicker plates very good cyclic performance can be are achieved, quite similar to that of a cyclic gel battery. Unfortunately, that does not detract from the fact that many AGM batteries in particular in recreational applications are, in fact, stationary batteries. These batteries will perform at best around 300 cycles, whereas a proper AGM DC battery will do 500-600 cycles, depending on depth of discharge.

TPPL (Thin Plate Pure Lead)

A further step development AGM is Odyssey® TPPL or Thin Plate Lead with flat 99.99% pure virgin – not alloy. Pure lead is made thinner, so it will fit the battery. More battery plates mean more plate surface area, which therefore means more power – twice as much as normal batteries. In fact, these batteries are capable providing engine cranking pulses in excess 2250 amps for 5 seconds – double, triple that equally sized conventional batteries, even at very low temperatures. They can also handle 400 charge-discharge cycles to 80% depth of discharge.

Also using pure lead, but with a quite different construction, are the orbital batteries of Cyclon, Genesis and Odyssey, featuring two long pure lead-tin plates wound into a tight spiral. This design is said to eliminate plate-to-plate movement and shedding of active mass.

Battery Type & Application

Lead-acid batteries can be subdivided into groups by applied technology, such as Flooded, AGM and Gel plus others that have been mentioned on these pages. Looking at the field of application is another way of categorizing batteries. Applications can be divided into three main categories and batteries are manufactured with these categories in mind. Each Category will have one or more battery technologies that are most suitable, plus a few cross-overs which will offer an alternative in less demanding applications.

Starter batteries – for starting combustion engines – have to release a lot of cranking power during a very limited period of time. Lots of relatively thin plates are the key to this, because they provide a large active surface for the electrochemical reaction to take place.

Deep cycle batteries – whereas the explosive discharge of a starter battery takes place at the surface, the electrochemical reaction during deep discharge goes on at a slower rate, but deep into the active mass until most of it is exhausted, notably at the positive plate. The charging and discharging of a positive plate involves lead sulphate, which is converted into lead dioxide and back again, since lead sulphate and lead dioxide have different molar volumes, a deep cycle battery is subject to a considerable change in volume during each cycle. It is no surprise that shedding of active mass is the main cause of failure of deep cycle batteries. The grids must therefore be strong, offering firm support to the active mass – which is why tubular batteries are so popular in this field: the active mass can’t go anywhere!

Standby batteries on the other hand are rarely overworked. They are waiting for an accident to happen and are designed to do so, under float charge, for a period of 5, 10 or even up to 25 years for a very expensive Planté battery. The design life of these batteries is for obvious reasons not expressed in cycles, but in years.

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