All About the Gel-Cell-Battery

What is a Gel-cell-battery?

The Gel cell has a solidified gel as an electrolyte, which is locked into each group of plates. During charging the Gel liquefies due to its thixotropic properties, and solidification after charging can exceed an hour as thixotropic gels have a reduced viscosity under stress. The newer battery types use phosphoric acid in the gel to retard the sulfation hardening rates.

How is a Gel-cell-battery constructed?

The lead plates in a gel cell are reinforced with calcium, rather than the antimony used in flooded cells. This reduces self-discharge rates, and they are relatively thin. This also helps gel diffusion and improves the charge acceptance rate as diffusion problems are reduced.

The separator provides electrical and mechanical isolation of the plates. Each cell has a safety valve to relieve the excess pressure if the set internal pressure is exceeded. The valve will then re-close tightly to prevent oxygen from entering the cell.

How is a Gel-cell-battery charged?

The gel battery has a higher charge acceptance rate than the flooded cell battery. This allows a more rapid charge rate and the typical rate is 50% of Ah capacity. A gel cell battery cannot tolerate having any equalising charge applied and this over charge condition will seriously damage them. During charging the current causes decomposition of the water and the generation of oxygen at the positive plate.

The oxygen diffuses through the unfilled glass mat separator pores to the negative plate, and chemically reacts to form lead oxide, lead sulfate and water. The charge current then reduces and does not evolve hydrogen gas.

If recombination of hydrogen is incomplete during overcharge conditions, the gases may vent to the battery locker. While these batteries will accept some 30-40% greater current than an equivalent lead acid battery they are restricted in the voltage levels allowed, so you cannot use any fast charging system.

The normal optimum voltage tolerance on Dryfit units is 14.4 volts. There are some minimal heating effects during charging, and this is caused by the recombination reaction. Continuous over or undercharging of gel cells is the most common cause of premature failure. In many cases this is due to use of imprecise automotive type chargers

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All about the gel-cell-battery and more