Hi Tom,
Do agree with all the replies. You need to know the battery capacity. If you are looking for the output of the charger make a provision of about 12 to 14% of the battery capacity for a 12 hour charger or 20 to 22% for an eight hour charger. Of course 12 hor charger is cheaper. We have these 2 types of chargers working in Singapore. The time taken to recharge the battery depends on the state of discharge. However, if I am not mistaken companies in the U.S. like to use the 8 hour charger. Of course the charger output must be the 36 VDC type, in your case