The 6 bay m18 charger chargers one at a time.. i have 1 at home and 2 at work. unless theres another model i dont know about, which is possible..
But it looks like there IS a 6 bay (3 m18 3 m12) rapid charger that WILL charge 3 batteries at the same time.. its THIS one.. now the question is - does it just do one SIDE at a time? I have a feeling that might be the case, but I’m not sure.. so it MIGHT do up to 3 m18 OR up to 3 m12 at the same time, but not mix and match.. i could be wrong.. I’d double check on YouTube, or ask Milwaukee customer service.
Edit: reading reviews it looks like you CAN charge m18 and m12 at the same time.. it looks like what you would need to do is load them so there is not anther battery directly across from it. This charger seems to be separated into 3 different ‘banks’. so from what reviewers are writing, if you loaded one side with an m18 at both corners,(middle empty) and the other side with just one m12 in the middle (both corners empty) - (or any arrangement where the port across from it was empty) it would work. (From what I’m reading anyway)
And it is a rapid charger.. so this one should do what you want, and its about the same $$ as the super charger.. might be worth the investment if your collection will grow.. OR just get a regular rapid charger and an additional m12 charger.. but if you dont mind spending the money - this is what you want, and you should see the same charge times as that super charger with the batteries you have.
https://www.homedepot.com/p/Milwauk...er-3-M12-and-3-M18-Ports-48-59-1807/205846387