A gel battery design is typically a modification of the standard lead acid battery. A gelling agent is added to the electrolyte to reduce movement inside the battery case. Many gel batteries also use one way valves in place of open vents, this helps the normal internal gasses to recombine back into water in the battery, reducing gassing. "Gel Cell" batteries are non-spillable even if they are broken. Gel cells must be charged at a lower voltage than flooded or AGM to prevent excess gas from damaging the cells. Fast charging them on a conventional automotive charger may be permanently damage a Gel Battery.
The newer type of sealed nonspillable maintenance free valve regulated battery uses "Absorbed Glass Mats", or AGM separators between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. These are also called "starved electrolyte.” Just like the Gel batteries, the AGM Battery will not leak acid if broken
The advantages of AGM batteries are no maintenance, sealed against fumes, hydrogen, leakage, or non-spilling even if they are broken, and can survive most freezes. AGM batteries are "recombinant" – which means the Oxygen and Hydrogen recombine inside the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost. Charging voltages for most AGM batteries are the same as for a standard type battery so there is no need for special charging adjustments or problems with incompatible chargers or charge controls. Since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. AGM batteries have a very low self-discharge rate (from 1% to 3% per month). So they can sit in storage for much longer periods without charging. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.
So anyone who is even thinking about going off road should seriously consider an AGM or at least a GEL battery for no other reason that to protect your bike in the event of a spill. All other riding Gods out there who will never ever ever possibly let their bike fall over even when parked in gravel or on the grass can carry on happily with a Lead Acid battery if they dare....
