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Location: Mauston, Wisconsin | Some small clarification on "Maintenance Free" Batteries. There are two basic types, 1.) Gel-Cell and 2.) AGM (Absorbent Glass Mat). The gel-cells were the first introduced for deep cycle applications (telco & Uninterruptible Power System markets). Like all things in life there are trade-off's. (should I date her or her sister?)
The Gel-Cell is just that, the electrolyte ( a mixture of hydrochloric acid and H2O found in your conventional wet cell battery) has been mixed with a gelling agent. This makes the battery non-spillable. If you're familiar with florist's gel, it has a similar consistency.
The AGM battery utilizes micro-porus glass mat's between the plates. These hold the liquid electrolyte like a sponge soaks up water. When they make a AGM battery its fully formed except the top cover hasn't been welded on. Then they fill the case with liquid electrolye, then after a short mount of time to allow the micro-porous mat's to absorb their capacity in electrolyte, they invert the battery jar and drain all the excess electrolyte. Then they electronically weld the plastic top cover on. Presto- non-spillable AGM VRLA battery.
The first problem with either Gel-Cell or AGM is that they have much lower tolerance for overcharging, versus a wet-cell where you can replenish the H2O (water). In a overcharge situation both gell & AGM have pressure release vents (typically ~ .5psi) . These allow the gases (hydrogen & oxygen) caused by overcharging to escape. Because hygrogen and oxygen are being lost, the electrolyte volume is decreased proportionately, as is the battery capacity. In the gell cell the gell drys out, in the AGM the mat dries out. The end results are the same, irreversible damage/lost capacity. No! You just can't pry the caps off & add water.
The other problem is related to low rate- long duration discharges. Discharging a battery effectively lower's the electrolye specific gravity. Never discharge a gell or AGM to less than ~ 10.5V or the manufacturer's recommendation. If you do, you may have a throw away battery, i.e., it may not be able to recover/recharge because the electrolyte is converted to almost all water. This is especially true if the voltage goes below 6V. So be warned - check your power switches at the end of the day.
Rader150- No! you don't have to worry about the gel burning up. But the battery can catch fire if you dry the gel out via overcharging. This is why I don't leave my charger on 7x24.
What I'm really saying is that gell-cell's and AGM's have a lower tolerance for abuse versus the conventional wet-cell battery.
That reminds me-> time to do a refresh charge on all three batteries in ESOX Maniac.
Have fun!
Al
Edited by ESOX Maniac 4/5/2006 2:50 PM
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