Thanks Pizzaguy. I owned a Chrysler Voyager for 20 years, so got firsthand experience of darn battery weirdness - and I went through many batteries. Probably an average lifespan of 2.5 years each.

I've subsequently discovered this battery in the Crossfire is just over a year old. It does seem unlikely to be a battery, but I'm sorely tempted to buy a new one. I can always keep the current one as a spare.