I'd vote for a bad connection somewhere. Batteries don't (usually) go ABM-dead and then recover. Your charge put 12 AH (amp-hours) in a 28 AH battery, not nearly a half charge (43%).
165W of lighting on a 280W alternator should not have affected it so catastrophically, but of the charging system is marginal, it might not be able to keep up. I like LED lights for conspicuity lighting, I save the Halogens lamps for nightime.
An on-board voltmeter is a good thing to have. I like the Kuryakin LED bar-graph meter.