Mike given the minimal age of the battery I would place it on a smart charger overnight set to AGM and possibly winter rate given present overnight temperatures. After waiting an hour to settle down after charge you should see 12.7 volts, maybe more due to residual surface charge. If its less and/or later drops as quickly as you suggest it's likely a u/s battery. Note that standing battery voltage is only relevant an hour or more after use or charging and is only then an indication of the state of charge on remaining capacity which could be a small fraction of as new. You could have a battery showing 12.7 volts standing but unable to start car when starter demands an unsupportable current draw due to minimal capacity.

As a side issue the reported starter problem is alarming in that it happens whilst vehicle is standing and needs to be investigated. Surely it would have triggered a recall though by BMW on their affected cars. It would be interesting to hear MMC's comments on this issue.


Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone