You recognize that your iPhone battery discharges very fast dispite you have a connected charge cable.
There could be many reasons:
- Wrong charge cable
- Additional Bluetooth/ WiFi activated
- Parallel used apps/ services
- Old firmware
- If you use a headset you can activate the screen lock. So you get only the navigation advices via headset and the screen will not discharge the battery.
- You should deactivate Bluetooth and/or WiFi if not needed.
- Deactivate all apps in the background (e.g. iTunes) if not needed.