Battery chargers are not suited to battery pack Voltage changes as they are made for charging only one Voltage of battery packs. A 36 Volt battery pack would require a 36 Volt charger, and a 48 Volt battery pack would require a 48 Volt charger. I do not know of any SLA battery chargers with a selector switch to charge different Voltage battery packs. Everyone SLA charger that I have seen is made for only one battery pack Voltage.
Kevin King