I Had this same issue when I bought a new battery. I charged the battery right up and then took it out and shoved it to the side for a week. Continuing to use my old battery, I then switched the battery back and it hasn’t restarted once and charges up and down perfectly (calibrated nicely). One think I did notice too was the ribbon cable wasn’t bent like my original apple one it needs to fold twice, I also did this but I can’t see that having much of an impact.
Hope it helps!