Just want to chime in that we had a recall on our Battery Isolation Module about a month after newly purchased in 2019 (Chateau 24F Ford E-350 chassis).
The scenario you encountered is exactly what was described as a "could happen" issue. It was replaced at the dealer for free under the recall.
Are you sure that metal box under the driver seat isn't part of the airbag collision system? I believe it's called a Restraint Control Module, which detects if the airbags have been deployed.
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