Phone is restarting, new battery installed twice.

My iPhone 6s Plus is randomly crashing and restarting, it seems to be worse when the battery is charged, and is horrible when charging. When the battery is low or actually stays on for a bit, up to 2 minutes when the battery is below 20 percent. At 100 percent it's crashing constantly often not making it long enough to enter the password fully. When it's about say 80 percent and plugged in it is crashing long before the password screen while the apple logo is still on the screen. Have taken it to a couple repair places and I've had the battery replaced once, it didn't fix anything, I replaced the battery again myself and that didn't fix anything. I've noticed that if I put it in the freezer it will power on and run till it warms back up. It's not overheating, seems like a high voltage issue or something? Is there a voltage regulator that I can replace? I have a panic log in was able to download a few months ago before the problem became so bad I can't keep it on long enough to do anything. I'm at a loss here and I need to get this phone fixed.