The battery should hold a charge for months if there isn't something draining it. Clocks take near nothing but, if it is a old style pulse solenoid type, it might remain energized if not working, in any event I'd unplug.

Do you have access to a clamp on amp meter? If not, disconnect one battery cable then place a 12 lamp from battery to cable. If the light is bright, start pulling fuses until the light goes out to isolate what circuit the drain is in.

If the light never goes out, disconnect the large wire on the alternator, then the small one. A shorted diode in the bridge or a regulator that stays on can cause a drain.