SLA Battery FAQ
| What is a gel cell battery or sealed lead acid battery? Gel cell or sealed lead acid batteries have basically the same chemistry as wet or flooded cell batteries. The batteries' electrolyte is in a gelatin form and is absorbed into the plates. The battery is then sealed with epoxy. These batteries may be used in any position. They are exceptionally leak resistant. Applications include UPS devices, emergency lights, and wheelchairs. These batteries contain 2 volts per cell with common voltages of 4, 6, and 12 volt. |
| Used terminology |
| [ Active Material ] This refers to the positive and negative plate pastes that provide energy from a battery when it is discharged. For a lead-acid battery, the positive active material, or PAM, is lead dixide; the negative active material, or NAM, is sponge lead. [ Ampere-hour ] The value obtained when the battery is normally used to define capacity of the battery. It is current in amperes, multiplied by the time in hours, during which current flows from the battery. [ Available Capacity ] The capacity available from the battery based on its state of charge, rate of discharge, ambient temperature and specified cut-off voltage. [ Battery ] Two or more cells, connected together, normally in series. At times, a single cell may be referred to as a battery. [ Capacity ] The electrical energy available from a cell or battery expressed in ampere-hours. It refers to the discharge of a constant current for a measure time to a specified cut-off voltage (normally 1.75V /2V cell), at a specified temperature. [ Capacity Recovery ] Also called recoverable capacity. This is the discharge capacity that can be restored to a cell or battery through various treatments when it had dropped to very low capacity levels. [ Cell ] The minimum unit of the battery that composes a storage battery; the nominal voltage of a cell of the Lead-Acid Battery is 2.0V. Most batteries are made of 2 or more cells. Typically 3 cells for a 6Volt, and 6 cells for a 12Volt battery. [ Charge ] The process of restoring electrical energy to a cell or battery, in the process increasing the cell voltage. [ Charge Efficiency ] Ratio of the ampere-hours delivered during discharge divided by the ampere-hours put into the battery during recharge. [ Constant Voltage Charge ] One of the charge methods which has voltage limitation. When the discharged battery is charged by this way, the charge current is reduced automatically according to the state of charge. This is the most recommendable charge method for VRLA batteries. [ Constant Current Charge ] One of the charge methods which has current limitation. According to the charge time, some fixed amount of capacity is charged. Therefore this charge method requires some devices which prevent overcharge such as timer etc., for VRLA battery. [ High-rate Charge/Discharge ] Charge / discharge processes that are carried out at relatively high current densities, with the multiple of C rate depending upon the battery design. [ Internal Impedance/Resistance ] A measure of a cell’s electrical resistance to current flow, resulting in small or large voltage drops and some level of resistive heating. Impedance (AC) and resistance (DC) values are proportional but different, resulting from differences in measurement methodology. [ Internal Short Circuit ] Positive plates and negative plates touch together through at the inside of the cell. [ Life ] The time period until the battery can no longer be used because it has lost its characteristics. [ Load ] A device or mechanism external to a battery, and which is powered by the battery. The resistance of the load and the battery voltage dictate the current flow rate, and thus the run time for the battery. [ Maintenance-Free ] Secondary cells that are not sealed require periodic addition of water. Sealed Lead-Acid Batteries do no require such maintenance. Therefore they are called “maintenance free”. [ Nominal Voltage ] A nominal value to be used to indicate the battery voltage; for the Sealed Lead-Acid Battery; the nominal voltage is 2V / cell. [ Open-Circuit Voltage ] The measured voltage of the cell or battery without a load attached. [ Overcharge ] The continuous charging of a cell after it achieves 100% of capacity. The battery life is reduced by prolonged over charge. [ Overcharge Current ] The charge current supplied during overcharge. Batteries can accept continuous overcharge at recommended rates and temperatures. [ Vent ] Pressure-relief valve in a cell or battery that allows for the escape of gases at some release pressure but does not allow any level of gas ingress. [ VRLA ] Abbreviation of Valve Regulated Lead-Acid. |