With a known good battery, what exactly happens when there is no start? Just a click? Nothing? Cranks but won't start? If just a click or nothing, then the connections are definitely the next logical thing to investigate.

A 765 cca battery is a bit small, but it should work if no other problem exists and outside temps aren't too cold. A 12.4 surface charge indicates about 85%, but that's not unusual off the store shelf. Probably good enough to get the car going in warmer weather, but needs a good run to get it charged up.

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'79 240D