I don't buy 12S (not sure if anyone even makes them). I have a couple 12S applications and use two 6S packs in series to make 12S. My current go-to lipo brand is RoaringTop (
www.roaringtopusa.com). Their 6S packs come with EC5 connectors, and I use this to make them 12S:
https://www.motionrc.com/collections...series-adapter