A necessary component of batteries, in conventional lead-acid batteries usually a diluted sulphuric acid, which is electrically conductive due to the ions it contains.
Electrolytes used for power generation are often liquid, but their properties can be changed by various additives. In gel batteries, for example, the sulphuric acid is bound in a gel-like manner by adding silicic acid. This battery class loses almost no liquid and is therefore maintenance-free or absolutely maintenance-free. In flooded batteries, on the other hand, the electrolyte level must be checked regularly and refilled with battery water if necessary.