Stu is right. For series 7 they allowed the voltage to go up to 50V, but it had to be true volts after charge. Therefore 48V SLA at 13.8V per battery would not be allowed (55.2V), but 3x 12V + 1x6V SLA for instance was ok (48 to 49V fully charged).

People were not happy with this ruling since it made it all a bit overcomplicated and no one ever made a problem of 36V being more than 36V.