I found that my UPS is not giving sufficient back up as expected for 20 minutes. I thought that I have to spend Rs. 800 to replace the battery. But I was not in a hurry. Want to find out the reason. After 5 minutes, the PC shutdowns. Why so? The UPS battery is not giving sufficient power (Ampere Hour) to run the load. The UPS battery is a 12 volt 7 Ah (Ampere hour) Maintenance free Sealed Lead – Acid battery (SLA). That means, it is “Maintenance free” and can be used for long time without any attention. But what happens is, the cells dry out due to heat generation. This happens after 6 months to 1 year of use . It is a Lead Acid battery that requires Electrolyte in the cells. So water is necessary inside. It has 6 individual cells giving 2V each. After removing the battery from the UPS, I found that it is very easy to rejuvenate the battery through “Hydration”. The battery will become top, if the dry cells are filled with battery water. Hydrated the battery and charged. Well, now it is giving more than 15 minutes back up. Saved Rs. 800 and reduced an e-waste. You can also rejuvenate the 6V Emergency lamp battery like this. So do it yourself. It is only a 10 minutes job.
So many factors. Battery needs care to maintain its chemistry and its energy efficiency. The aging process starts at the moment the battery leaves the manufacturing factory. Self discharge ,sulphation, capacity loss, overcharging, dendrite growth, grid corrosion, excessive heat and water loss etc are some common reasons for the premature battery failure.
If the battery is not cycling for long period, self discharge takes place @ 4 % per week at 27 degree. For example, a 125 Ah battery shows self discharge @ 5 Amps current per week if it is not discharging through the Inverter. Sulphation is another important factor affecting battery efficiency. The lead sulphate accumulating on the plates prevents charge release/ acceptance cycles. Usually the lead sulphate crystals will be removed during water filling and charging. So it is better to charge the battery as soon as possible to prevent sulphation.
Another important reason is overcharging. The battery used in backup systems should have a charger cut off facility, otherwise the battery will get over charged due to float charging. When the battery is overcharged, the charge voltage increases above the Gassing voltage. This causes formation of excess hydrogen. The Gassing voltage of a 12 V lead acid battery is 14.3 at room temperature. The battery voltage crosses the gassing voltage level if one or more cells are damaged or weaker. The weaker cell will charge last since its resistance is lower than the good cells. So higher voltage appears across the good cells and may increase the voltage above the gassing voltage level.
By using the battery equalization method, it is easy to make the battery fully charged. All the cells in the battery will not be equally good due to aging. Some cells accept charge very fast and some in a slow rate. If this happens, the battery will not hold sufficient charge and will discharge very fast through the load. Equalization is done by giving slight overcharge to the battery even after the terminal voltage rises to maximum. Due to this overcharging, the weaker cells also get time to accept full charge. A fully charged 12 volt lead acid battery will show 13.8 V terminal voltage and a 12 V tubular battery will show 14.8 V in the fully charged state.
12 Volt battery used in vehicles is the Lead Acid (LA) type battery which can deliver more than 45 Ampere current to ignite the engine. It is the type of Starting battery or SLI battery (Starting Light Ignition) designed to give a heavy current to start the engine. The lead acid battery is composed of series of plates immersed in a solution of Sulphuric acid. Each plate has a Grid on which the active material is attached. In the negative plate, lead oxide is attached as the active material while on the positive plate, pure lead is attached. All the negative plates are connected together and connected to the external negative terminal. Similarly all the positive plates are connected together and with the positive terminal.
The electrolyte in the battery is sulphuric acid- water mixture which has specific gravity. The specific gravity is the weight of the sulphuric acid- water mixture compared to equal volume of water. Pure water has a specific gravity of 1.
During the battery discharge, the sulphuric acid in the electrolyte combines with the active material of the plates. This releases energy and the plate material becomes Lead sulphate both in the positive and negative plates. When this happens, hydrogen atoms of the sulphuric acid combines with oxygen to form water. As a result, positive plates release electrons and the negative plates accept equal number of electrons. This creates a potential difference between the positive and negative plates and current passes through the load.
During the charging and discharging process, heavy chemical reaction takes place which changes the specific gravity of sulphuric acid .This can damage the plates and may reduce the charging holding capacity. To prevent plate drying, topping with desired quantity of distilled water is necessary.