Where does ather energy buy lithium ion battery from?

with my little experience in lithium ion batteries i think these guys are making their own battery pack with combination of good quality 18650 lithium ion cell connected in series and parallel combination to reach required voltage and capacity respectively (ex. 48v and 60ah battery pack). which is pretty much easy with some spot welding machine and ton of experience.

The thing here is, are they making there own battery management system(BMS) or they buying it from other source(my hard guess there most possibly designing there own circuit).