All indications are it's weak. The problem with assuming vs further testing is that often the starter is at fault.

If you have a multimeter that can measure peak voltage, measure the voltage from cig Lighter to the B+ under the hood while starting.

It should read about 0.75 v when first start and abiut 0.65v for a restart (if oil still in the journal bearings).

Many cases of "weak battery" turn out to be dying starter (they will pull up to double the current as they die).

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)