For 48V lithium batteries, the charger should be 54.6V charger, because the full voltage of 13 strings of lithium batteries is 54.6V, which means that any battery 48V lithium battery can be charged with this charger, but the charging time is 54.6V. This is different.
The charger does not match. Just like if you use a 5V 1A charger to charge your 5V 2A cell phone, it will take a long time. charge.
Normally, the 48v12A battery is charged with 1.8A and the 48/20 battery is charged with 2.5A. Low current means charging is slow. I can deal with this