It is a bit simple relative to the battery type needed.
If the "EE" Hyster unit was purchased from the factory with side panels (designed to be compatible for "EE" rating) and side panels are still installed (they often get convienently lost over time) then a standard battery can be fitted.

If the unit was purchased without side panels then a "EE" battery with cover, etc would need to be installed.

It would always be a good idea to check with the Hyster or their authorized representative (local dealer) w/ model and s/n in hand to be on the safe side. There may have been a factory design update since the unit was first shipped.
Be further advised, it is possible that a component such as a switch, accelator control, directional controllerhas been replaced with a non EE rated component do to sourcing or price issues. This means that the UL EE rating would be voided

Kevin from UK
"EE" rating referes to a rating established by Underwriter's Laboratories working with NFPA (National Fire Protection Agency) for equipment that can work in hazardous enviorments. Basically, the EE rating requires the drive, steering, and hydraulic pump motors to be totally enclosed; battery terminal be enclsoed (either with compartment side panels or battery cover) contactor and constroller panel to be sealed, ground strap and other similar changes or sealants to prevent spark emission from the lift.
EE is not the same as EU standards. EU is closer to the ASME B56.1(American Society for Mechanical Engieers) which defines the lift truck design with a plathora of should (meaning a good idea to do it) and shall (you better do it cause everyone else in the business will do it)statements.