My 24k service was $422, However, it did not include an overnight battery check. I don't think my dealer has ever checked the battery, and probably doesn't know how. It was the usual oil change and heavy on the drivetrain inspection, plus brake service. I think my dealer likes working on brakes, which tells you where their technical expertise lies.
It does seem that Mitsubishi needs to up their oil game. My old Subaru went 10k on synthetic oil. My wife's Audi A3 e-tron goes 15k between changes, same Canadian climate.