Chosen Solution
With my 6s+ the battery went from 90% to 1% and restarted itself over and over, and then wouldn’t charge. I thought the battery was to blame so I replaced it. It worked good for a day and then its back to 1% and restarting. Now, its stuck in a boot loop were it will go between quickly flashing the backlight and flashing apple logo. Any ideas? Ive tried to restore but it doesn’t stay on long enough. Also, when I first opened the phone 6 months after buying it on eBay, the battery connector cover was missing. I read online it could be the battery sensor. Any ideas?
Try applying some pressure down on the connector while the phone turns on. If it works fine then you just need the metal bracket. If not then you might be missing some components near the battery connector which are commonly knocked off when preforming a battery replacement.
I think you need the battery connector cover, the battery ribbon cable plug may have a loose connection to the battery connector on the board requiring that metal cover that goes over the battery connector and charging port connector. iFixit sells the battery connector bracket here: iPhone 6s Plus Battery Connector Bracket Here is a guide in case you need it: iPhone 6s Plus Battery Replacement
