As others have already mentioned you need a better charger. I use a wireless air dock charger that is rated at ~800mah charging rate and it keeps my phone slowly charging up(3% every 5-6 minutes) while screen is on using gps navigation and streaming Google music through Bluetooth.Your phone actually charges in the car? If I'm using GPS, a car charger just makes my phone die slower haha even in my 12v input
Get a charger that's rated at least 2.1 amps or a quick charger if your phone is compatible with it, charges my wife's lg g4 from zero to hero in about 40 minutes.