Phone turns off after 2-3 mins

I just swapped out my old iPhone 4s battery. everything went well. Put everything back together. it stayed on the whole time while lowering the battery to 10% to start recharge. During recharge i noticed the phone going off and on nonstop. I've done hard resets several times. Once it was 100% i unplugged and and tried but it still just shuts off after 2-3 mins and will start right back up.