Batteries are a painful topic, if you do a search on the forum questions you’ll see there’s someone having troubles every day, especially with aftermarket batteries. Your Mac runs off charger only too, thus you have an easy testing tool available, just unplug the battery from the board and see what happens. If it’s a battery issue the Mac will boot on its own and allow normal operations as soon as you connect the magsafe charger, in which case just ask for a battery replacement. If the issue is still there..well, let’s hope it’s not there to start with ;)