Glad you got there in the end.
Modern car batteries don’t like going flat, and if AGM are fitted they are very intolerant of it.
![Mad :x](./images/smilies/angry.gif)
. If the battery has been flat for that long then it may have been damaged, or at the very least it’s service life will have been shortened. If it still doesn’t show at least 12.6V after fully recharging then a cell has died. 0.67V indicates cell sulphating, and possibly an open-circuit condition.
See how it goes, and the best thing to try now the panic is over is to put the charger into its reconditioning mode ‘Cond’ and leave it. That mode gives the battery a high voltage ‘kick’ that is intended to get the sulphates off the battery plates and allow normal charging to start.