Z4...battery tender question
Have used a Sears battery tender(regularly on sale for around $20), on my 2003 Z4, 2.5. Prior to buying the Sears unit, I checked out the BMW one and was told by the BMW sales manager to just buy the Sear product at 1/4th the price of the BMW one.
Prior to moving to Florida this past winter, the car was in residence in Upstate New York, parked in my cold garage, with the Sears battery tender on it for 4-5 months at a time. In the Spring, it always started up at first turn of the key. Now that I can drive the car daily, I will charge the battery, through the cigarette lighter plug, once a week.
I've had my now 7 year old battery checked regularly and informed it's still as good as new.
I believe the Sears Battery Tender is engineered and produced my Schmacher(not Michael).
Gor for it...it's cheap insurance that your battery won't let you down.