That is BS, they do not have a setting to limit the battery to 80%, no doubt some have dodgy batteries, I have been lucky as they 99% of the time charge to 100% and drain at the same time and die within a few secs/1min at most of each other, on a rare occasion 1 side (can be either) does not charge fully and drains faster (I clean the contacts often).
My only real issue is the AMB leaking in with ANC enabled 90% of the time (sometimes it works fine) since the last FW update.
