The classic lead battery uses liquid sulfuric acid as electrolyte. In the event of accidents or incorrect handling, this can leak out and cause damage. For this reason, and because they require less maintenance, sealed lead batteries have been developed in which the sulfuric acid is bound.
This type of battery is called Valve Regulated Lead Acid( VRLA). There are two VRLA designs: The gel or lead-gel battery, VRLA-Gel, and the lead-fleece battery, VRLA- AGM. In the gel battery, the Sealed Lead Acid( SLA), the sulfuric acid is bonded in a gel with silica.
The SLA battery consists of individual battery cells and is completely encapsulated. It is not refilled with water. During normal charging, recombination takes place by electrolysis between the hydrogen and oxygen produced at the electrodes, which is over 99%. The charging voltage is about 0.8 V higher than the nominal voltage. In the case of rapid charging or overcharging, there may be an excess of hydrogen that does not recombine with the oxygen. To remove this hydrogen, the SLA battery has safety valves for degassing.
The internal resistance of gel batteries is more than 20 milli-ohms, which is higher than that of lead-fleece batteries, but the number of charge cycles and, above all, the service life are higher than those of conventional batteries. As for discharging, with a nominal capacity of 1 Ah, this can be done in just a few seconds with a high current of 20 A or 40 A .
Rechargeable, valve-protected gel batteries can be used in leisure products and garden equipment such as children's cars, soap boxes, model cars, e-scooters, quad bikes, wheelchairs and lawn robots. But also in smaller UPS systems to provide electrical power for some time in case of power failure.