I believe they use the starter (I'm not sure how you'd fire the next cylinder without using a starter to move the piston- the stroke goes fuel spray, compress, fire - so you can't simply ignite fuel that's sitting on the cylinder walls and you can't have it spray and compress without moving the piston - so no matter what you need a starter to get that going...)

Bear in mind it's not your typical ignition starter - a start/stop starter has much greater mass AFAIK

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01 m5 - 118k miles 1/2013....08 535xit - 85k miles