In lead–acid gel batteries the sulfuric acid is mixed with finely divided silica, which forms a thick paste or gel. The freshly mixed gel is poured into the cell container before it sets. As the gel dries microscopic cracks form that allows the passage of gas between the positive and negative plates required for the recombination process. This formation of cracks may occur during the early part of a gel battery’s service life, so both hydrogen and oxygen can be given off from a new battery through the safety valve. At high operating temperatures they will suffer to some extent from water loss, but since there is more acid than in an equivalent AGM battery, the lifetime reduction will not be so severe. Attention should be paid to the manufacturer’s instructions concerning this, especially regarding ventilation requirements.

Gel batteries have low rate capacity (C20 to C3)

The self-discharge, especially in the absence of phosphoric acid, is very low: initially, the capacity loss is <0.1% day−1 and, after 2 years of storage, <30% (e.g., for a 100 Ah battery).

Gel batteries can be deep discharged, i.e., discharged below the specified cutoff voltage in extreme cases or down to zero volt, which will lead to a small capacity loss only after recharge.

Endurance in Cycling; Gel batteries achieve a cycle life up to 1000 cycles with 75% depth of discharge depending on design, especially of the positive plate (tubular or grid plate), the electrolyte composition, and the cycling regime.

Gel batteries are robust against variations in the charging regime and the state of charge