Tristar tester saying “ battery not connected” when I checked and know

That it is connected and has proper battery voltage.I replaced the battery and lighting/audio connector assembly. Besides display not coming on. My tristar tester says the battery is not connected with the display connected. But with it disconnected says it is present. Prior to this , this phone stopped working. I redownloaded the phones programming including updates. Then the phone worked but wouldn’t bring up the screen for me to enter my second verification codes to include it in my apple id. So I thought there was a problem with the lighting connector and decided to replace it and the battery since it was over five years old. Any thoughts…battery voltages are right where they are supposed to be. So I don’t think the battery is bad. But could there be a short in the display to make it not even see the battery once it’s connected to the tristar tester ? So I’m wondering if there is a fuse kinda thing that would cause this to make the tester say it’s not connected ? Thanks for thinking about this with me ….