Why is my iPhone5 shutting off and on while chargeing?

So here is what is happening I bought this phone off a friend and it starting acting up, when I charge my iphone 5 the phone shuts off and then back on again over and over again until the phone is charged fully, around every 3-5 minutes it shuts off and back on through the whole charging process.

I replaced the battery and found out that this phone had water damage, my so called friend never told me about this when selling me the phone !(Liquid Indicator was RED)

Also the battery percentage is not correct it will show 100% and then I restart the phone and it shows a different percentage?

The phone has also been shutting off and back on every 5 minutes or so even when not charging any ideas ?

*I have already replaced the battery with the iFixit kit.

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*I have done a hard reset ,full restore ,update etc.

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*I did the battery calibration process but still shows wrong %.

PLEASE HELP NOTHING IS WORKING :(