I think a significant number of people use their iPhone for navigational purposes in the car but they also have a charger that can be plugged in while the phone is being used for active GPS connection.
I see. That makes more sense. Have you looked into those dynamo powered batteries?! Not sure if you still get them these days. Keeping it constantly on for 5-6 hours everyday does increase the chances of burn in. This is not a typical use case for an iPhone X I’d assume.
I drive from Dayton OH to Cleveland with no issues. 3 hour drive. Never paid attn to the percent of drain. Going there in a couple weeks will try to check it out.
Disable True Tone in Settings > Display and reduce the brightness if possible to increase the battery life. It should be long enough in this case.
Regarding the display, I agree with @akash.nu, the chances of burn in are much higher and it will happen faster. Could be better to get some older device if possible.