That tends to lean towards the alternator being or going bad. I have had the same thing many years ago,

https://www.dsmtuners.com/threads/battery-brake-lights-on.523873/#post-153729157

https://www.dsmtuners.com/threads/b...icker-on-off-dead-alternator-merged-4-8.2082/

There is also a small wire with plug that goes on the alternator somehow mine got unplugged as they are barely on there. I believe it has something to do with helping to control the idle, I had higher idle until I found out why and noticed it wasnt connected. But does sound like bad alternator or battery going out. Weird why lower then normal operating voltages will cause stuff to freak out. My 2011 135i bmw the windshield wipers would flap like crazy with a dead battery even with the wipers off .