Battery Drains extremely quick even in standby and airplane
My iPhone 5s is less than a year old and the battery one day started draining incredibly fast even in standby and airplane. I tried to reset the phone and set up as new with no luck. I've tried doing all the "hacks to save battery" such as turning off mail fetch. But the battery still drains very fast. The phone aloso can charge to 100% but is never "fully charged" so I am unable to check the standby and usage times in battery settings. I also have noticed that my phone doesn't charge on car charges at all and charges slow on regular USB wall outlet chargers. I've read about the U2 IC chip causing similar issues but if my phone dies it has no problem charging and booting back up. So don't know if that still could be it. Lastly I do notice the phone gets a little warm sometimes even when it just in standby mode untouched. Any help would be greatly appreciated.
UPDATE: took into a repair shop and tried a battery change. After the battery change my phone wouldn't charge!? So we tried another battery replacement but didn't work so we put the old battery back in and it started charging again? Still no results and stuck carrying a portable charger around still.