i dont know about the battery thing but most leaks come from the windshield. the gasket is easily caulked with black silicone. you need to clean it really weil first with alcohol or such and make sure it is dry. i do it on all my old benzes... well, you know... all my benzes ARE old. i wouldnt drill a hole... it will let water in as well as out. IMO.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.