What do you wish to calculate ?
Circuit ampacity of each branch circuit ?
Feeder ampacity for a number of battery chargers ?
For each branch circuit, I would follow the suppliers instructions, after making some simplified calculations in case there is a typo or mistake in these instructions.
For a feeder that suppliers a number of battery chargers, I would simply add up the actual input of each battery charger.
If the chargers are relatively slow chargers and therefore likely to run for more than 3 hours, then upsize to 125% for the continous load.
If they are fast chargers and complete the chargeing cycle in less than 3 hours, then a simple total should be sufficient.
If the current input is very variable, then it MIGHT be resonable to allow a smaller feeder ampacity on the grounds that not all the chargers will use the maximum at the same time.
For charging a company fleet of EVs, it is likely that at the end of the work day all chargers will be in use at the same time, at full capacity.
For charging a number of privatly owned EVs in say a parking lot, it is unlikely that all chargers will demand full power at the same time.
Some chargers may be unused, or connected to vehicles that are nearly charged.