Hi Tom, to calculate charger size you will need to look at the battery data plate and check what the AH/C rating of the battery is. (Ampere/Hour Capacity) usually stated as being at a 5 hour rating) Then as it is a 36v battery it will be easy for sombody to work out the charger size for 3 or single phase. We have 240 single and 400 3 phase in the UK so our calculations will be inacurate for the US. But I am sure if you post this info one of the other guys will come back yo you when they sober up after the holiday.......Happy New Year everybody, Dave