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With both Air and MagSafe battery at 100%, it uses the Air until its battery is 90%. Then it starts using the MagSafe battery. The Air’s battery stayed at 90% until the MagSafe battery was depleted.

Good to know. That might be a nice option for when I travel (as opposed to letting phone battery deplete and then using the MagSafe battery to try to top it up).
 
Still trying to decide about returning the Air. Snagged a 17PM to cross test. PM battery lasted a long time to 4% with moderate use.

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