GPS or Google Maps?

I don't know of any restriction on where you mount the GPS in Italy. FWIW, we rented a car in Verona last month and asked for a GPS as well. (I seem to recall that they call those a "navigatore" and the one they gave us was a Tomtom.) Once we got it and started using it, we kept getting a message on the display saying that it had not been updated in 27 months. There is currently a good bit of road construction and re-routes in Verona so that proved to be a bit of a problem. Bringing your own GPS with you will ensure that the information is current.

Bring your own navigator from the US. Purchase and Load EU maps in it. Renting a GPS navigator from the rental company will increase your rent by at least 10 euro a day. Google maps works, but you'll need wifi to access it from a computer, ipad. If you rely on your smartphone i don't know if it needs to have the data roaming enabled. I have never used the GPS feature on the smartphone outside the US. When I travel to Europe I turn the data roaming off because the data roaming charges cost hundreds of $$.

'keeping the GPS active for a long trip impacts battery life.' Not if you hook it up to the lighter socket like any other gps.

That's certainly true, Ed. Thanks. So one would need to come prepared with an adapter that has vehicle lighter connector on one side and USB on the other, plus the needed USB --> smartphone cable.

Which is exactly what anybody has who charges a phone in the car. Nothing special.

But the little adapter is an easy thing to forget to bring and perhaps not available from the vehicle rental agency at the last minute. Then precious time could be wasted trying to buy one. Speaking from unfortunate experience. :/

Thanks for the advice! I think I am going to play it safe. I just ordered a GPS. So, I will be covered regardless. But I am also taking my smartphone and I will download some Sicily maps before I leave and try google maps in offline mode as well.