Stage pianos sometimes have no speakers.

Last night in the UK on Top Gear they had Eric Clapton plug in an electric guitar into the Aux in socket of a car and played it through the speakers of the car system. I've done this with my phone on a old Honda.

Would this actually work? Not to power the stage piano itself just to get some usable output?

Granted the sounds would probably be poor as car speakers are probably built down to a price even more so than digital pianos.

Might be an interesting way to gig...

I'm sure it would work though remember to unplug the cable before driving away.

An aux in is an aux in, but it would probably sound very boomy and indirect. The best place to listen to a stock car stereo is from within the car, so I wouldn't think it would sound great from outside the car even with the doors open. But yeah it would work.

You could power most digital pianos from your car with a small power inverter, available at most big-box and auto parts stores. Sounds like the whole idea would be kind of a novelty, though.

Boomy and indirect...... like a concert grand perhaps?

Interesting