Internal self-balancing for li-ion 3S pack


I am building an electric car which will have solar-charge feature.
Main power supply for my PCB is 12V (3S li-ion cells).

Now I have two options but I don't know what is better and more commonly used:

  • buy some RC battery which has extra wires for balancer while charging
  • build own pack from 18650 cells and add there some cheap BMS

My pack will be charged from solar panels on-board so there must be balancer connected all the time. But I have read that this will self-discharge battery in some days/weeks.

  • is a better idea to disconnect balancer with some relays while not charging?
  • or is there some balancer which can do this for it's own?

Which balancers do you prefer (brand, model) if I would need it as IC on my PCB?

And last question, is it OK if there is load (20-100 mA) on battery while charging? I found many forums where people say, it is OK and many forums where people say that it will confuse the charger. Can you please explain what is true and why?

Thanks for all your advice!