Robin used his keyboard to write :
JOOI do motorhomes separate the battery from the distribution circuits when
connected to the mains? I ask only as I wondered if it might work out
cheaper to fit (a) a "Smart" battery charger (£20) and (b) a separate 12V
PSU (eg LED driver). Also avoids single point of failure.

They use a system of the battery supplying the load, with a charger/PSU
in parallel with the battery - so PSU is able to both source the load
and charge the battery. Some of the later PSU are able to act
intelligently in their charging of the battery. I seem to recall some
have a link able to be set, for the various battery chemistries.