The Gel battery is well suited for use by amateurs to supply backup power in the event of a mains power failure. There seems to be a lot of these batteries around at the moment and the second hand price is very cheap. Most of these batteries are removed from service when they start showing a fall off in capacity and thus turn up on the surplus market. The best thing about these batteries is that they do not emit much gas if any when being recharged correctly. Recharging voltage should be 14.05 volts with an absolute upper maximum of 14.40 volts. Charging at a higher voltage causes the silica based electrolyte to swell and cause plate distortion. This renders the battery useless in a very short period of time.

The gel batteries are sealed and can be placed in any operating position as the gelled electrolyte stays locked between the battery plates and does not move. To revive a battery that shows loss in capacity due to the terminal voltage falling rapidly on current draw you must first get into the battery. The vent caps on most batteries can be popped off with the help of a screwdriver and the actual vents can be unscrewed using a correct size spanner. Once the vents are taken out have a look at the top of the plates to see if they look dry or moist. In most cases they will look dry.

The revival of the battery is pretty easy, just add distilled or de-ionised water so that it covers the plates by 10mm. The trick is to now load the battery so that after an hour or two the voltage discharges to 12 volts. Let the battery rest at this level for a couple of hours and then recharge to 14.4 volts. Check the water to see if it has been drawn into the electrolyte. If you have a millimetre or two on top of the plates then you have revived the battery. If the battery has taken all the water then add more water and repeat the process. Put the vents back into the battery and glue the vent cover back on with a few dabs of hot melt or epoxy. The battery capacity will improve over the next few charge discharge cycles