New to ring, do the battery switch need to be on when connected to house power 120v
Yes, the converter is a battery recharger, and charges the battery when connected to shore power. If the battery disconnect is off, then the battery cannot be recharged.
Unless your TT is stored you should leave that switch on.
That might be true, but the question was posed in the Motorhomes > General Motorhome Discussion > Forester and Sunseeker forum, so I don’t think a TT is involved here.
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2020 Sunseeker 2440DS on 2019 Ford E-450, Trekker cap, Topaz paint
OP didn’t list the model number. Some Forester/Sunseeker models will lose power to some 12 volt items even if connected to shore power (ac) if the battery is disconnected.