I just followed the ifixit instructions to replace my battery with a new one. It will not boot when the power button is pressed. If I hook up a thunderbolt power cable it will boot and run very slowly. The battery icon shows an “X”. I have tried resetting both the SMC and the PRAM. I don’t if it actually reset them, but I have followed a few versions of instructions to do so. I will hook up a volt meter to the new battery tomorrow to see if it has a charge maybe. Pretty frustrated. If anyone has any ideas please let me know. Thanks!!!