I know very little about Faraday cages (I do hope you’ve put a hole in the wall for the muffler of the generator) and I always store my stuff with the batteries disconnected. Keeps the posts from getting all cruddy. If you have an electric start one, I’d learn how to Farady it. I would also look around the net for better info than I.
Portable generator & transfer switch are outside. Just had the genny overhauled. It’s been a big help in power outages in the past.
Only need it infrequently, so, of course, we always forget the maintenance and battery charging until we see an adverse weather forecast. Biggest drawback: it hates really cold weather, so we haul it inside to warm up as needed. We get by fine overnight with lanterns and wood stove and just need to remember not to flush w/o power.
Longest usage of one smaller than the current one was 9 days. We were just selective about what we used. It serves 2 buildings, so we have to balance that, too. We have good wood heat w/ a masonry chimney (we burn out the stove pipe every week in season),a couple of portable propane camp heaters, battery LED lanterns, 12-hour hurricane candles, a charcoal grill and a couple of different camping stoves (butane). Most important, IMO, is well and sewer pump. It does fine w/frig and 2 chest freezers. We have a wet cellar w/a sump pump and a collection of electric pumps. Very essential in warmer weather here in a river valley discharge area. Those are the vital basics. If we have advanced warning, we heat the hot tub to max before turning it off. It holds heat very well over a couple of days if propane hot water heater conks out. My freezers are generally full, but if I know we’re in for a storm, I stuff in water bottles for the coolers or just for xtra drinking water. I keep the 2 500-gallon propane tanks at least 1/2 full (usually more) at all times and at least one winter’s supply of firewood. So far, we have good neighbors, too.
Food stores, safe year-round piped spring,xtra meds....that’s about it and has served us well the past 43 years.