BATTERY TECHNOLOGY IN A NUTSHELL

CLASSIFICATION BY PLATE MATERIAL

Pure lead

The original lead-acid battery was invented in 1859 by French physicist Gaston Plant�.

The basic principle and chemistry behind modern batteries is still the same. However, improvements in construction and the addition of various doping elements to the plates have transformed the battery in terms of performance, reliability and case size.

The plates in a modern battery are formed from grids made of lead containing traces of metals such as antimony, calcium and silver. The grids hold the active lead/lead oxide paste which makes the battery work. The characteristics of the different doping materials on battery performance are described below.

Lead-antimony (Sb)

This is the traditional car battery of the late 20th century.

Advantages:
- The primary reason for adding antimony is to improve the mechanical strength of electrodes, especially important where the battery is used in a moving environment.
- Compared with a lead-calcium battery, this traditional battery has a longer service life
Disadvantages:
- Compared with a lead-calcium battery, this battery has a higher self-discharge rate, typically 5% - 10% per month. This is a particular disadvantage where the battery sits for a long time between charging.
Voltage set-points for a 12v battery: alternator charging: 13.9v, bulk charge: 14.3v, float voltage: 13.2v

Lead-calcium (Ca)

By adding calcium instead of antimony to the lead used to make the grid, both electrical and mechanical improvements can be achieved.

Advantages:
- The addition of calcium increases the battery gassing voltage, in the case of a 12v battery by about 0.5v.
- The less gassing, the less electrolyte loss, the less the need to top up the electrolyte, i.e. 'low maintenance'
- Lower internal leakage currents, meaning the battery self-discharges much more slowly. This increases the shelf life of the battery, typically by 50% or more.
The technology is at the heart of so-called 'low-maintenance' (sometimes incorrectly referred to as �maintenance-free�) batteries that do not require the electrolyte to be regularly topped up with distilled water. However, this is misleading in that if the battery is regularly charged at the proper voltage there will still be some gassing and electrolyte (actually water) loss. This raises two problems which are mutually exclusive:

Disadvantages:
- Constant undercharging will occur when a lead-calcium battery is used with a charging system designed for a lead-antimony or hybrid battery. Such a battery will never become fully charged. The life and performance of a battery is significantly reduced by extended periods in a partially discharged state, due to both sulphation and electrolyte stratification.
- In order to prevent the electrolyte stratification mentioned above, the usual method is to use an equalization charge from time to time. The purpose of the equalization charge is to purposely create gas bubbles by charging at above the gassing voltage. The gas bubbles mix up the electrolyte, eliminating any stratification that may have occurred. Gassing �boils off� some of the water in the electrolyte, which needs to be replaced by topping up, which may or may not be possible in a �sealed� battery. (All �sealed� batteries have vents to ensure that a gassing battery cannot build up an excessive internal pressure.)
Voltage set-points for a 12v battery: alternator charging: 14.8v, bulk charge: 15.2v, float voltage: 14.2v

Hybrid antimony/calcium (Sb, Ca)

The positive grid is strengthened with antimony, and the negative grid is strengthened with calcium.

The hybrid has the advantage of the lead-calcium battery in terms of lower water loss, and the advantage of the lead-antimony battery in terms of better resistance to deep cycling. It also shares to some degree the disadvantages of both battery types.

On the surface this seems to be quite a clever idea, but in reality the lead-calcium battery has more to offer at a similar cost, so the hybrid is not the battery of choice today.

Voltage set-points for a 12v battery: alternator charging: 14.4v, bulk charge: 14.8v, float voltage: 13.7v

Lead-silver-calcium (Ag-Ca)

The electrical performance is similar to lead-calcium.

Advantages:
Disadvantages:
Voltage set-points for a 12v battery: alternator charging: 14.8v, bulk charge: 15.2v, float voltage: 14.2v

BATTERY CONSTRUCTION

Flooded cell

The battery plates are immersed in cells filled with electrolyte. A removable cap allows distilled water to be added to the electrolyte from time to time. Typical of the lead-antimony battery.

Sealed / �low maintenance�

The construction is essentially the same as the flooded cell battery. Removable caps, which also contain vents, may be hidden behind a sticker proclaiming �low maintenance' or even 'maintenance free�, or a cover plate of some description. These caps allow gas to escape during the normal use of the battery. As gas is produced, so the electrolyte level drops.

Ideally, the electrolyte level should be checked every now and again, and topped up as necessary to maximize the life of the battery, which means exposing the removable caps.

So where possible, remove the sticker or cover plate to expose the removable caps. This may invalidate the warranty, so best do it when the warranty has expired, although in some cases this may be too late.

VRLA

The construction of a Valve Regulated Lead Acid battery is similar to the �low maintenance� battery, with the addition of a recombinant catalyst. Unlike the removable caps of a 'low maintenance' battery, valves permit a positive pressure of a few psi to build up in the battery as it gasses. This pressure, in conjunction with the catalyst, causes a high percentage of the gas to recombine with the electrolyte, thus minimizing electrolyte loss.

Above a defined pressure gas is allowed to escape, so over time the electrolyte level will slowly decrease, but at a much lower rate than with a �low maintenance� battery. There is plenty of room for confusion between sealed / �low maintenance� and VRLA batteries, although price will usually indicate which battery you are dealing with.

Gel

The electrolyte surrounding the plates is suspended in a gel, which is usually formed by adding silica. A gel battery is genuinely sealed and requires no topping up.

The big plus of gel batteries is that they are spill-proof (although clever cap design can achieve almost the same thing for flooded cells). In addition electrolyte stratification is unlikely to occur.

By its nature, the charging currents are lower than for flooded batteries, since gel batteries are easily damaged by overcharging. Consequently, charging times will be proportionately greater.

AGM batteries appear to offer all the advantages of a gel battery, since the electrolyte in both batteries is held in place, but none of the disadvantages.

AGM

The principle difference between an AGM and flooded battery is that the electrolyte is held in a porous glass-fibre mat. Like the gel battery, electrolyte stratification cannot occur due to the immobility of the electrolyte. This means that:
AGM batteries are correctly classified as 'maintenance-free', and have many advantages over the other types of lead-acid battery:
The overall performance of AGM batteries is the best of all the different types of battery, in that the CCA is significantly higher than an equivalent flooded battery and the recharge rate is also higher.

The AGM battery is the clear leader in terms of electrical performance and longevity. However this comes at a significant cost.

BATTERY USAGE

Starter battery

This takes its name from its traditional use in vehicles to start the engine. Originally, battery power was also required for the ignition system and lights.

Modern vehicles require battery power for a whole host of functions, from the dashboard clock to engine management computers and entertainment systems, putting a strain on battery capacity and charging systems.

The fundamental purpose of a starter battery is to provide short bursts (a few seconds) of high current (300+ amps) to the engine starter motor. Once started, the battery charge should be quickly replaced by the charging system so that the battery spends 99% of its life fully charged.

The construction of the battery reflects this type of use: thinner plates with more surface area provide the high starting current while sacrificing the robustness required of deep discharge batteries.

Deep discharge battery

A deep discharge battery is designed to provide battery power for an extended time between charges. An electric vehicle that charges over night and drains the battery power during daytime use is a good example of this. Deep discharge batteries are also used for stand-by power: here the batteries are kept fully charged by an external power source and are only discharged in the unlikely event of external power source failure.

The construction of the battery reflects this type of use: thicker plates of a sturdier design sacrifice surface area for rigidity. The available current is lower, but the ability to sustain multiple discharge/charge cycles will result in a reasonable service life.

COMMON PROBLEMS

Sulphation

This affects all the different types of battery, including gel and AGM.

The rate at which a battery becomes choked by sulphation depends on many factors, but one thing is certain: all batteries suffer sulphation to some degree. Statistically, sulphation causes the failure and replacement of 84% of all batteries, so it is reasonable to say most batteries are significantly affected. By controlling sulphation, a significantly longer battery life along with enhanced performance can be expected.

Sulphation causes the progressive deterioration of battery performance in terms of maximum current capability, ability to charge up quickly, and the amount of power stored by the battery, all the signs of a �weak� battery.

Keeping sulphation under control is therefore fundamental to long-term battery performance.

Megapulse is an electronic battery desulphator which eliminates the sulphation problem entirely.

Read more about sulphation here

Electrolyte stratification

This affects all the different types of battery, excepting gel and AGM.

The primary cause of stratification is where a battery sits for long periods in a partially discharged state.

The conventional way of eliminating stratification is by periodically applying an equalization charge. This is a process that must be done with care, because overdoing it can easily result in warped plates and dead cells.

Read more about electrolyte stratification here