How does going on a long road trip strengthen a car battery? And do long road trips really filter out gunk from car engine?

How does going on a long road trip strengthen a car battery? And do long road trips really filter out gunk from car engine?
1) Long trips will do very little for your battery. The batteries only function is to start the engine. After that the alternator does all the work. Once the engine is started and the charging system has recharged it, the battery does little more than complete the circuit.

2) Long road trips won't "filter out gunk" though you may burn up a bad tank of gas. If you need to clean your engine internally, there are many products mechanics use to do the cleaning that are far more effective and can pin-point individual systems.

Check your engine drive belts and your tire pressures.