At least 4x a year somebody on xo either can't start there car or had some horrible electrical gremlin happen after long term of dead battery. Zero percent chance I would leave and BMW without a battery connected other than momentarily to replace it. (many will hook up a maintainer or parallel battery at the b+ during the swap to never have the voltage drop)

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