What Bert said above was the cause of my wife’s ipad pro 2015 restarting about every 3 minutes. I replaced the battery in her ipad pro 2015 and it appeared to work fine. Then, after about 3 minutes it would restart. I followed Bert’s advice and disassembled the ipad again and inspected the springy pins on the motherboard that connect it with the battery. One of the small pins was not aligned perfectly with one of the small contacts on the battery pad. Also, the flexible battery pad where the battery contacts are located seemed to lay a little too flat. After creating a small stack of tiny pieces of sticky notes and placing them under the flexible battery contact pad and adjusting it slightly to align the pins a little better, the contacts were aligned with the motherboard pins. After reassembly the ipad works perfectly. My wife is very happy to have her ipad working again.