If you want a cordless vacuum designed for repairabilty, there is a new company called Lupe which is trying https://lupetechnology.com/
Vacuum wars were impressed at least https://youtu.be/rFbkGM9Lm18
No idea about battery balancing in them though, maybe I need to open it and try to find out. My gut feeling is that they wouldn't save out on a few resistors.