Unlocking/locking the doors in quick succession certainly drops the voltage quickly. I sometimes leave a Noco charger connected for days at a time which will happily display Green -ok. Unlock the doors and it plunges to to Red and starts charging. I haven't checked the BM2 data in a while, but I noticed similar behaviour to your report. Also to anyone who hasn't had a flat battery yet, don't sit in the car and run anything on Acessory mode. The voltage drops rapidly and the battery will fall below 12v.