Just caught up with this
@brucemillar - damn ssl certs and house renovations have kept me on my toes over the last few weeks.
First of all, the battery needs to be tested. If it is a wet battery, which it should be, check the state of charge with a hydrometer. Yes, it’s old school (but so are we) but that will give a much more accurate indication than a voltmeter.
If it is low charge, then assume either a charging problem (unlikely given what you have said) or a battery/starter circuit issue.
Despite the devices that inject an ac current into the battery to test the internal impedence being de rigeur these days, I prefer to do a load test on the battery. You can get a much better idea of how it is performing, and a ‘boiling cell’ and smell of ozone will give the game away.
Both the hydrometer and load testers can be got cheap enough, or a reputable auto electrician - not someone who’s best interest is to flog you a battery - should be able to test this.
Once this is determined and you have a known good battery you can investigate parasitic discharge or starting circuit (or possibly charging) - I’ll post up the process, but as has been alluded to, the alarm circuit is a known source of battery drain, especially with an old smoker such as yours.
The one strange thing is that the car has obviously started earlier in the day, and these types of problem usually manifest themselves with the first start and a cold battery/engine.
