How should I wire up a 3 prong dryer outlet to 120V?
DO NOT wire a 10-30R receptacle to 120V, and a "standard" 120V 15 or 20A receptacle CANNOT be put on a 30A circuit. If this unit is capable of being run on 120V then there will be instructions on how to convert/wire it. There will be a way to replace the plug on the unit with a standard 15 or 20A 120V plug. You may also need to re-wire it internally. 

Can you post the name and model of the charger? More info may be available online.