The maximum charging current for a single 8D is .3C or .3*250AH or 75 amp maximum charge current.
I have 12 batteries in total wired for 48VDC?
For a 750AH system I would recommend a 25%*Ah or .25C rate which would be .25*(750Ah) or 187 amps maximum charging current and a minimum charging current of 75 amps(.1C).
Please remember when placing batteries in series or parallel or both to make sure the charger gets into the float stage and stays in float a minimum of 4 hours minimum to balance the batteries.