What you should know about batteries!

What is a battery?
A battery can be described as an electrochemical device that stores energy in chemical form. When it is attached to a consumer the chemical energy is transformed into electrical energy.

All batteries consist of one or more cells. Each cell is built up of positive and negative electrodes, with a separator and an electrolyte. The most common are lead acid batteries, which have a nominal cell voltage of 2 Volts. A 12 Volt battery consists of cells connected in series.

The active material in the positive electrode consists of lead dioxide. In the negative electrode the active material is a porous sheet of fine grained lead. The electrolyte is a diluted sulphuric acid. These components are put together in different ways to create batteries suited for various tasks.

Function of the battery
When a battery is discharged or charged an electrochemical process involving the active material of both electrodes takes place. At discharging, the lead sulphate is built up on the negative as well as the positive electrode at the same time as energy is emitted. When charging energy is supplied and the chemical process is reversed. The lead sulphate returns into the original lead oxide and fine grained lead. This process must be as complete as possible in order for the battery to become fully charged. If the battery is over charged, water is consumed and a highly explosive mixture of hydrogen and oxygen gas is produced.

Discharging
The energy that a battery produces can be specified in different ways, depending on what purpose the battery is used for. Starter batteries are often specified in CCA or Cold Cranking current in Amperes (Amperes a battery will deliver for 30 sec in -18°C without the voltage dropping beneath 1,2 V/Cell). For other types of batteries in the most common denomination is Ampere hours (Ah) which specifies how many Amperes the battery can give in a certain time without voltage falling below a specified value. The capacity for Leisure batteries are mostly given as C20, which means the rate in amperes a battery will deliver for 20 hours with the voltage not dropping below 1,75V/Cell. If a battery under these conditions delivers 4 Amps it means that the capacity will be 4Ax20Hrs=80 Ah. Batteries used for industrial purposes are often designated using the C5 capacity. This means that an 80 Ah battery will give 16 Amps for 5 hrs. The same battery would, if discharged with a fixed current for 20 hrs give a higher current than 4 Amps. The level of discharge current thus has an influence on capacity, a higher rate of current means a lower capacity rating. Also the temperature will have an influence on capacity, a higher temperature on the battery, within limits, will give a higher output.

Charging
The efficiency of the chemical process in the battery means that the energy supplied must be bigger than the useful energy output from the battery. It is important that the batteries get exactly fully charged. All the lead sulphate must be processed into lead oxide in order that the electrodes do not sulphate, which is what happens if the battery is undercharged. If the battery is overcharged water is lost through gassing, which will cause corrosion of the electrodes. Overcharging can also cause the battery to rise above allowable level and damage the battery.

The battery state of charging can be measured using an acid tester that will measure the specific gravity of the battery fluid. Another way is to use an accurate voltmeter. A sealed Lead-Acid battery can only be controlled using the voltmeter.