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Hi, My iphone 6s shows charging symbol. but bat % not increasing beyond 4. tried another fully charged battery. still shows 4%. tried dfu mode and hard reset. It keeps on restarting after a few mins(5-7). How to diagnose the problem?
You’ve already done a pretty good job diagnosing the issue. You tried a known working battery, you tried resetting it, those are great first steps. Now you are down to basically 2 things it could be: Lightning port or power IC. Its more than likely the power IC since they are known to go bad but the Lightning connector would be the cheapest and easiest thing to try. iPhone 6s Lightning Connector and Headphone Jack iPhone 6s Lightning Connector Assembly Replacement
