What are the differences between AGM and Gel batteries?

Both are recombinant batteries. Both are sealed and valve-regulated and are considered non spill-able and both are considered “acid-starved.” The electrolyte in an AGM or gel battery does not flow like a normal liquid. In AGM batteries all liquid electrolyte is trapped in a sponge-like matted glass fiber separator material. In a gel battery the electrolyte is mixed with an additive that changes it into a gelled consistency.

The “acid-starved” condition of gel and AGM batteries protects the plates during heavy deep-discharges. The more acid starved, the more protection to the plate.

Due to the physical properties of the gelled electrolyte, gel battery power declines faster than an AGM battery’s as the temperature drops below 32°F. AGM batteries excel for high current, high power applications and in extremely cold environments. If you have a gel battery that performs better than its equivalent AGM in cold weather use, the odds are the gel battery is utilizing thinner plates and higher specific gravity acid and/or an increased volume of acid or acid to active material ratio than higher quality gelled batteries. It may be less acid starved than the AGM comparable, is probably not a true gel battery design, and may actually be what is referred to as semi gel (essentially an AGM battery with gelled electrolyte material located only at the upper regions of the cell).

Flooded batteries are more easily replaced by AGM batteries than Gel batteries as Gel batteries require different charging algorithms (mainly lower finishing voltages) to excel and live than do either AGM or Flooded types.

Note that the difference between Gel and AGM batteries for higher current, high power applications is very small until extremely low temperatures are experienced. Please see the section “Temperature affects a batteries available Capacity”, later in this document.