Um, if you have to, you can make it work.
Best for the string of batteries to be open-circuit for the time you're charging them, and get them ALL to the same charge before connecting them back up.
Preferably the same current at the same float voltage.
Then use 'em up...
Then repeat the whole dreadful process again...
My turn for a stupid question: Whatcha doing with 48V without a proper charger?