The unit of SoH measurement is percent , 100% SoH level, the new battery’s health according the battery’s specifications.
As the batteries are used, a process degradation remaining capacity of the battery.
For example, if the State of Health (SoH) of a 100 amp battery is 80%, then this means that its real maximum capacity is 80 amps. And above this capacity, we will not be able to charge it..