Need help, 12V battery

I am new on this forum, so if i do somthing wrong tell me asap =)

I do have a el-bike.
48V, 1000 W motor.
I have serie-connected four 12V car (gel) batteries to it.
This work werry well, but the problem is, it’s so hard to charge the batteris.

I use a 12V-Car charger. I disconnect the batteries, and connect them in parallel. Charge it up and change back to connectien the batteries in serie.

Is there, any other way? like can i use a 48 V charger, or is it an easier way to do it ?

Thank you :slight_smile: