From what I have read on them you use a normal battery. But I haven't seen any reference to gel cell batteries and how those would be affected.

The technology works simply by charging the battery at 3-5 times the normal charging rate for a short time, generally during lunch breaks and short periods of forklift inactivity. When you are charging a battery at 400 to 600 amps, damage to the battery is possible so read all instructions and follow them.