3 Lead Acid battery types. What's the difference?

There are 3 main kinds of Lead Acid batteries.

• AGM stands for 'absorbed glass mat' where the electrolyte is soaked in a glass mat around the lead plates
• Gel batteries thicken the electrolyte into a gel which stays relatively immobile around the plates
• Flooded batteries use liquid electrolyte flooded around the lead plates without obstruction

The way the electrolyte is held inside the battery creates small differences between the types. Flooded batteries tend to have the highest voltage, the highest current capability, are the least expensive to make, and carry the highest capacity. But because the electrolyte sloshes around inside the case, it has to stay upright, and the electrolyte level often needs to be checked and refilled. And if the case is cracked, sulfuric acid will gush out.

This last problem is so bad that gel batteries were invented to solve it. And gel batteries are almost as good in performance as flooded types in voltage, current capability, and capacity. So they would be ideal for a lead acid application... except for cost. Creating and constructing a gel type lead acid battery is expensive and for that reason, there are not many made.

AGM batteries were created to solve the problem of cost, and indeed they fit the niche well. And their performance is so close to that of a gel battery that people will frequently use "gel" and "AGM" interchangeably. Although almost anytime you hear someone call a battery a "gel cell" it is really AGM.

So one would think AGM would displace gel batteries and flooded types as well. Since they are "almost as good" in performance and they don't carry a hazardous liquid risk. Except, again, for the cost. And even a little performance difference matters. So even though AGM will only be a little more expensive and give a little less performance... people would rather pay a little less and have better performance. And the risk in many situations is not great when using flooded batteries.

So we'll see flooded batteries in situations where the case is protected and the battery is not bounced around. And we'll see AGM types where the battery can be picked up or turned over or bounced around. AGM batteries are also better for situations where ventilation can be a problem. We'll also see AGM where checking water would raise maintenance costs above the cost of AGM.

And even gel batteries are still made in small numbers for special applications, frequently in higher temperature situations.