I presume that you want to modify the MX350 to run on 36 Volts? If this is your plan then the MX350's original 24 Volt charger will need to be replaced with a 36 Volt battery charger. However if you plan to keep the bike running at 24 Volts then the original charger will work with the new batteries.
Please let us know if you have any questions.
Tony