Hello fellow E70 owners! My 09 E70 N52 just hit 140k miles, and I had pretty much everything changed on that vehicle: water pump/thermostat twice, starter, belts, gaskets, etc. The only part that should have failed already, but hasn't so far is the alternator. I take my car on long family trips quite often and am always scared of getting stranded, and so I am considering preemptively changing the alternator.

I found a good deal on FCP Euro for remanufactured Bosch alternator (under $300) and there is $100 core charge, but I am not sure how to proceed and looking for your opinion. Here are the options I am considering:

* Don't do anything
* Buy an alternator and put it in the trunk for just in case.
* Buy an alternator, replace it, and put old one in the trunk as a spare.
* Buy an alternator, replace it, return old but working alternator, and get $100 back.

What should I do?