Chosen Solution
Due to poor battery life, I decided to replace the battery myself. After putting in the new battery, the audio doesn’t work (there’s no internal speakers available), the system is slow, the MagSafe light doesn’t turn on, and the battery didn’t charge past 42%. I decided to put the old battery back in but the only thing that fixed was the ability to charge to 100% (no MagSafe light comes on still). I tried to reset the SMC already. Any suggestions for any of these problems? I returned the battery and have one from this site coming. When I get a new toolkit with the new new battery, I plan on making sure I didn’t unintentionally disconnect anything else in there!
I had exactly the same problem after changing my battery (audio not working, magsafe light off, and tremendously slowly system). I tryed also Smc reset without success. Finally after checking it was a bad connection of one of the cables that are below the fan (in my macbook air mid 2012). Just press down a little and solved… I hope this will help you.
