2020 Keystone Hideout. Safe to unhook battery? full timers

What oldbiscuit said.

Of course you can unhook them. Are you asking if it’s ok to unhook or ok to run the trailer without batteries?
Be more specific in your questions.
BTW, you need a battery because that’s how the camper is designed. Even if plugged in, many of the systems are DC current.
Can’t help with the electrical smell. Nothing you did would have changed an existing condition.