The problem with dealer battery comes when you need to swap it for warranty. In hot climates like FL, batteries often die in 3 years. I can't speak to MB dealers, but the Dodge dealer was unacceptable on a Mopar return: no simple swap, had to bring the car in (tough to do when the battery is fried) so they could test the charging system. Not worth it for a pro-rated refund.
Our local Home Depot is now stocking car batteries at attractive prices. I'm wondering how their exchange process will be.

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Prost!