Just a note of interest -- I buy my batteries from SAM's Club, average price $56. I had a Champion 1050 battery in my Dodge Caravan for 9 years (yes I said 9 years) before it required a jump. It never leaked and I leave that van out in the driveway 365 days a year in Chicago's hot/freezing climate. I visited SAM's when I purchased my ML about 3 months ago and found they recently began stocking a ML320 replacement battery for around $54.

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Slowdriver

2000 ML320 (37K Mi)
1985 BMW 735i (155K Mi)
1989 Caravan (102K Mi) cargo hauler
2000 Montana (40K Mi) family hauler