I have noticed that there is some benefit to charging 12V AGM batteries individually vs. charging them in series for 24V, 36V, or 48V scooters. This is especially true of they are mismatched in age, Ah rating, true Ah, and/or health. My friend has this condition where his 48V scooter uses 4 different batteries and they never seem to charge right (some overcharge and some undercharge) using the 48V charger.
Carrying multiple chargers around with you is a hassle so a reasonable compromise would be to charge using 12V chargers at home and maybe take the 24V, 36V, or 48V charger with you on long scooter rides where you would have an opportunity to charge away from home.
Another reasonable compromise is if you do not want to purchase four 12V chargers for a 48V setup, just get 2 of them and charge 2 batteries at a time. That will keep the cost down and it is good to have two 12V chargers anyway in case one fails, so you can still charge all the batteries individually.
Many chargers will even allow you to charge 12V batteries individually without having to break the series connection, on a 24V, 36V, or 48V battery bank which is a real convenience. Take advantage of that.