My mid-2013 13” MacBook Air had been running like a champ but the battery began showing a “replace soon” warning a few weeks. I received the new battery I ordered today so I shut the computer down and opened the back to replace it. The Air was running great with nearly 100% charge. Turns out the new battery didn’t fit (a tad small) so I place the original back in. Now the computer won’t show any signs of life! I tried powering it with the old battery plugged in and unplugged, tried all kinds of resets but absolutely nothing. The power adapter lights amber and green like everything is normal but the thing won’t start at all. WTF did simply unplugging the battery and plugging it back in do??