I have the same problem. I replaced the battery with an iFixit battery about a year ago. It has been running fine until today when the battery is no longer being recognized. I don't know if it is a software problem (Latest Mac OS refuses to recognize aftermarket batteries) or if the battery is now defective, of if there is a hardware problem with the power circuitry. When I boot the Mac (Air 13" early 2015) the battery symbol has an X in it. When I look at the System Report, it shows that the Full charge capacity is 0 and that the cycle count of the battery is 0. When I run Coconut Battery app, the app dies.