williamwright pretended :
Following the suggestion here that the charging voltage for Circuit C was too
high
("C: 14.6V, +0.01A")
I checked with an accurate meter. The voltage was 13.86V. That accords with
the very low residual charge rate. As I suspected, the van's voltmeter is
reading a bit high.

Bill

My caravans limited range analogue voltmeter is in the panel, by the
door - some way from the battery. It's reasonably accurate for an
analogue, but the daft part is that they have shared it's supply with
everything else - it measures across the main feed. Absolutely anything
you turn on, will cause voltage drop and the reading to decline
drastically. The only way to get a true reading, is with the main
isolator on, the rest of the isolators off and use a torch in the dark
to read it.