If you have a decent data tariff and smartphone I would use Waze. Waze were purchased by Google some time back so now a lot of their function is actually built into GoogleMaps. I love Apple but cannot recommend Apple Maps sadly !
If you don't want to use your data tariff you can get an app which has full maps on board such as Navmii so can run standalone. Not as clever as Waze but just as good as most stand alone devices and easier to keep to up date free of charge.
The nice thing about phones is that the cost and availability of car mounts is much greater. Also the range of apps gives you more choice on smartphones. One thing to carry and charge, lots of uses outside of the map (which pub, best price, petrol station in distant places, SOS etc)
If you are worried about the battery life on a long run then get one of the smaller battery packs that give it a constant charge and can be recharged from any USB charger at the destination. These can give 24 hours permanent running. Something like this,
http://www.ebuyer.com/668008-kensington-power-bank-k38220ww 
