Chosen Solution

I put the new battery in 2/20/18. Charged it 3/4 full all worked fine,Sat,Sun, & got very low & battery showed about 8% charged. Today is 2/22/18 & it cut off early so I charged it for about 2 hours to a full charge. Now it cuts off after about 10 seconds into a call or checking messages,or safari .love my kit & want to keep trying till ifixit.thats a good pun!please let me know what to try next. Thanks

Which iPhone is this? And this is usually due to the battery going faulty.