A battery is a device for storing electrical energy in a chemical form, and then releasing it as direct current in a controlled way. All types of batteries contain a positive and a negative electrode immersed in an electrolyte, the whole assembly being within a container. All batteries are a lead-acid battery, which means that they have positive and negative electrodes made of lead compounds in a dilute sulphuric acid electrolyte. Lead-acid batteries are secondary batteries, which mean that they can be recharged after they have been discharged. Primary batteries can be discharged only once and then have to be thrown away.
The positive electrode is made of lead dioxide and the negative electrode is made of porous lead. When an electrical load is connected across the battery, a current flows through the electrolyte in the battery and through the external load. This causes the battery to discharge, which results in the chemical composition of both the electrodes changing to lead sulphate. A battery can be charged by putting a current through the battery from an outside source of electricity such as an alternator, dynamo or charging unit. This converts the lead sulphate back to the original materials of lead dioxide and porous lead. As the battery becomes charged, the electricity begins to decompose the water in the electrolyte into its constituent elements of hydrogen and oxygen, which are released as gas. This is why a battery gases when it is charged.
As the positive and negative electrodes are made of weak materials, they need a mechanical support which is provided by a grid made from a lead alloy; lead on its own would be too soft. In addition to providing a support for the electrodes (the active material), the grid also conducts electricity from the electrodes to the outside load
The electrodes are initially made from a mixture of lead oxide and lead sulphate, and this is converted into lead dioxide in the positive plate and porous lead in the negative plate when the battery is initially charged.
The negative electrode also contains small amounts of additives to give the battery a good discharge performance at low temperatures to improve starting. The combination of grid and electrode is normally called a plate.
The electrolyte is dilute sulphuric acid. This acts as a conductor to transport electrical ions between the positive and negative plates when the battery is being charged or discharged.
The acid also takes part in the discharge as the sulphate ions react chemically at the electrodes to produce lead sulphate.
The separator is an insulator placed between the positive and negative plates to prevent them shorting together.
The separator needs to be microporous with very small holes to allow the ions to flow through the separator from one plate to another. It also needs to be able to resist the high temperatures and strongly acidic oxidising conditions that occur in a battery.
Most modern separators are made of microporous polyethylene, which has suitable properties to meet the demanding conditions within the battery.
Container and Lid
These are normally made of polypropylene, which is a light but strong plastic. Unlike some plastics, it does not become brittle when it is cold, and so can resist knocks during handling. It is not attacked by acid and it can also withstand the fluids (petrol, diesel, brake-fluid, antifreeze) normally found on a vehicle.
Proper battery selection may require the assistance of a knowledgeable battery sales/service technician. Please contact Europower Battery Centre for advice.
A deep cycle battery has the ability to be deeply discharged and charged many times during its service life. It is designed specifically for powering electrical equipment for long periods of time.
For applications where both engine starting and light deep cycling are required, a dual-purpose battery is often used. This type of battery is neither a starting nor a deep cycle battery but rather a compromise between the two so it performs both functions adequately.
AGM batteries absorb the battery acid in the glass fibres and thus binds it in. Since the electrolyte (acid) is contained in the glass mats, it cannot spill, even if the battery is broken. This also means that AGM batteries are non-hazardous. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage. The plates in AGM’s are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.
The AGM battery has an extremely low internal electrical resistance. This, combined with faster acid migration, allows the AGM batteries to deliver and absorb higher rates of amperage than other sealed batteries during discharging and charging.
Nearly all AGM batteries are “recombinant”. This means that the oxygen and hydrogen recombine inside the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.
The charging voltages are the same as for any standard battery; therefore there is no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents.
AGM’s have a very low self-discharge – from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries.
Liquid levels should be 1/8 inch below the bottom of the vent well (the plastic tube that extends into the battery). The electrolyte level should not drop below the top of the plates.
Under normal operating conditions, you never need to add acid. Only distilled, deionised or approved water should be added to achieve the recommended levels mentioned above. Once filled, a battery should only need periodic water addition.
The only way a battery can freeze if it is left in a state of partial or complete discharge. As the state of charge in the battery decreased, the electrolyte becomes more like water and the freezing temperature increases.
You will reduce the frequency of watering but will cause a condition known as stratification where the specific gravity of the electrolyte is light at the top of the battery and heavy at the bottom. This condition results in poor performance and reduced battery lift.
A solution of baking soda and water. Use 1 lb of baking soda for every gallon of water.
Lead acid batteries are 100% recyclable. Lead is the most recycled metal in the world today. The plastic containers and covers of old batteries are neutralised, reground and used in the manufacture of new battery cases. The electrolyte can be processed for recycled wastewater uses.