try unplugging the wire on the altinator, get a multimeter, put meter on
continuity, place one probe on altinator body and check the pins in the
altinator with the other probe, if you get a reading you probably have a
earth fault. Also with the altinator plugged in place the two probes
across the battery and make sure you are getting around 13v charge,
possibly the battery is not holding charge does the car start ok next day?
Normally an earth fault would drain the battery overnight, check battery
terminals are tight and body earth leads.