Thanks for the advice everyone. Some good lessons here.
We took the battery out and put it on an automatic charger. The initial charge was 2 amps. The following morning I went to the hangar to check up. The charger indicated 0 amps, 12.8 V and FULL. We put it back in the aircraft and started up. Normal start and normal-looking charge rates. Perhaps we got lucky. An experienced colleague suggested that the life of the battery might be significantly reduced. We’re going to keep a close eye on the battery performance.
An unexpected bonus to this episode was that my colleague was going to an impromptu fly-in lunch, that had been arranged at short notice to celebrate the current VMC after two weeks of miserable weather. So I tagged along in the back seat of a Scout. We met up with the occupants of an RV-8 and an RV-7A at a nearby airport, and walked across a golf course for lunch in the club house.
A lovely flight in beautifully smooth conditions and no navigational challenges - even TCT could have done it. Only 25 minutes by Scout and one of the RVs was less than 15 minutes from our destination. Definitely a $100 hamburger flight!