in the USA, the _current_ standards for forklifts are "owned" by an organization that calls itself "The Industrial Truck Standards Development Foundation" [itsdf] and in the USA we can access their standards by agreeing to a few very reasonable things after searching for itsdf dot org.
The Battery industry has it's own set of standards, as does the ieee for electric motors, cables, connections, etc. and the UL (somewhat like CE in Europe) for insurance ratings.