Garmins as mentioned above. The Edge range while have maps on the higher end and are nice, are more oriented to performance and training. The other stuff may be more rugged.
Will get good battery life from a dedicated device.
If you want to try a phone, or use one for back up or something, I recommend ViewRanger for maps. Can buy OS maps for it, but can use free OSM maps also which are just as good plus have additional things OS may not have. Licence for VR transfers to any device and you can sync routes and stuff between them and web account.
Can also transfer GPX files between various devices, web, and transfer them to as Garmin as a route to follow.