I was cursing the stubby little points on the test leads the other day causing access issues so I started looking at another set to replace them. on close inspection they unscrew!
If it's still dying check that the heated rear screen is not on and that the warning light has died .
Though I'd have given the battery a 12 hr charge using a desulphating charger as I have one . Quite a few times what has been a condemned battery has been suffering from years of gradual sulphation on the plate .
on BMW's we had things like the heater blower starting on its own during the night, or something stopping it going to sleep (low current draw standby) what does mr Google say?