Hello,
Do you know how old the battery is to begin with? Does this 'smell' smell like wires possibly melting? Maybe something is making contact against a hot surface where it shouldn't be. It's been a while since I've been on here but aren't the camshaft position sensor wires a trouble area for melting/getting brittle because of heat? Have you heard any squealing/shrieking leading up to this smell recently? Check the accessory belts for abnormal wear to help rule out an accessory bearing starting to seize. Hope you find your problem and that it's not a PITA.

Jes