What are the differences between AGM, Gel and Flooded batteries?

Wet batteries do not have special pressurized non gassing sealing vents as they do not work on the recombination principle.  They contain liquid electrolyte that can spill and cause corrosion if tipped or punctured.  Flooded batteries are only transportable as hazardous materials and they cannot be shipped via Express Courier or Parcel Post  and should not be used near sensitive electronic equipment and they can only be installed “upright” Because of the cost associated with maintenance including man-hours; service materials such as distilled water and cleaning agents; corrosion related repairs; damaged clothing; special gas/air exchange systems in charging areas, and pollution related environmental issues in areas where flooded batteries are being charged and/or discharged, wet batteries may actually cost more to own over the life of the battery than do high quality AGM or Gel batteries which are normally more costly to buy.

Some brands of wet or flooded batteries are also marketed and sold as sealed or maintenance free, but they are still flooded cell batteries, they are  not “acid-starved”, they are not considered "Non-Spillable" for transportation purposes and and they DO NOT have the same pressurized non-gassing venting system.