MacBook only powers on with adaptor, doesn't detect new or old battery

Hi

I had exactly the same problem recently with a Mid 2012 13" Macbook Pro and tried all the steps you mentioned.

Turned out that I had a broken battery sensor (flat connector on the bottom right hand side of the logic board which is connected to the button on the right hand side that shows battery power level)

After disconnecting this connector and doing (yet another) PRAM and SMC reset, the Macbook started working. Will be ordering another battery indicator cable but for now leaving it unplugged. Charging light went orange and it detected and charged the battery right up to 100% and has been sitting running on battery power for hours now with the battery indicator cable disconnected!

Also another thing to make sure is that you have the latest SMC Update installed , as SMC version 1.5 did resolve battery issues. (And SMC v1.8 on the 2012 model)

https://support.apple.com/kb/DL1474?loca...