Notsosane

We recently put a new battery on our 2017 Spark and it immediately went into reduced power mode and had all kinds of codes and lights on the dash. We had it “diagnosed” at the dealer and they said it was either the ECU or the fuse box. The ECU would be covered under warranty and the fuse box wouldn’t. They wouldn’t even consider the ECU until we paid to have the fuse box replaced and if that didn’t work they would then change the ECU. Has anyone ever heard of a fuse box going bad?