Phone GPS apps can work well, but they do zap the battery. Quick. I run an app called Backcounry Navigator Pro. It is really nice and works as accurately on my Android as any dedicated GPS. It even stores offline maps for when out of cell service.
If that is all you have, there is a work around to save battery life. This also works with a GPS where the battery is almost dead. Some phone apps and most handhelds will store waypoints. The waypoint lists will store the name, the distance from your current location and bearing (degrees) from your current location.
All you need is a decent baseplate compass. Decent Suunto's or Bruntons are less than $20. Just let your phone or GPS aquire a satelite lock to update your current location. Go to your listed waypoints and find the distance and bearing to your intended destination. GPS or phone app says: "Truck-1.2 miles-bearing 124 degrees". Dial in 124 degrees on the compass, turn off the GPS or GPS function on the phone to save power and follow the compass for a mile. When close to the target turn the GPS or phone GPS back on and finish finding the destination if needed.
Note that the only real hitch with this is for folks who are in an area with a high varience with magnetic declination. Study that in a orienteering book or online.