Flooded versus AGM Batteries?

Both flooded and AGM batteries contain electrolyte mixture within the battery that's comprised of approximately 35% sulfuric acid by volume. So, approximately 35% of that liquid inside the battery is sulfuric acid.  
Flooded batteries have excess electrolyte or free-flowing electrolyte within the cells that cover the cells usually by 1/2 to 3/4 inch or cover the plate by 1/2 to 3/4 inch. And flooded batteries are known for off-gassing during charge and discharge operation. So, while the batteries are discharged or charged they give off hydrogen gas. This hydrogen gas is known to be explosive and corrosive so care must be taken when working around flooded batteries to ensure there's no sparks or open flames and that we wear the proper safety protective equipment such as eyeglasses and rubber gloves.  
AGM batteries on the other hand have all the electrolyte absorbed in their separators. So, they have thick absorbent glass mat separators in between the positive and negative plates. We only have enough electrolyte in that battery that all of that electrolyte is soaked up into those glass mat separators. This means no free-flow acids sloshing around inside the battery. This also means that the batteries are non-gassing. So, during normal charging and discharge the batteries do not emit any off-gas. They do however have rubber valves in the vent caps that if there's too much pressure built up it'll allow that pressure to bleed off so that the battery doesn't bulge and wanna blow up, essentially.  
So, some of the advantages and disadvantages to flooded batteries are they're less expensive. The technology's been around for years and years and they're widely available. It's the least expensive battery technology there is. The downside is they're considered hazardous material or dangerous goods. So once again, care must be taken when working around them and when shipping these types of batteries. We must insure that we have the proper dangerous goods paperwork and the proper certifications for handling them. 
AGM batteries on the other hand are slightly more expensive. These prices have come down in the last few years but when it comes to automotive starting batteries we're seeing them more common and more available in the market today, The upside is they're considered non-hazardous material as they don't off-gas during normal charge and discharge operation so we don't have to take the same safety precautions as far as paperwork and handling are when we're dealing with AGM batteries.  
So for more information on flooded and AGM batteries watch our vide on our YouTube Channel here.