Do some research on parallel charging. I parallel charge all the time with my multirotors.
Check out Joshua Bardwell on YouTube and his parallel charging videos. Very informational.
I currently have 2 turnigy Reaktor 250w chargers on a 750w power supply. I can charge 12x 1300mah 4s lipos all at once and have 12 batteries ready from storage to full charge in roughly 40 minutes.