g'day
where to start . firstly do you want hand held or a mounted one . a hand held one comes with batterys which are just manily aa size . get one that best fits your needs eg car boat or bushwalking . from there it gets a little easier a gps uses saterlites for finding it self so the more of them it can get the better off you'll be eg 4 , 6 , 8 ,12 . get one that will keep as many waypoints (marks ) as possiby and as many routes ( a number of waypoints put together to form track eg: beacons at you local ramp so at night youcan find your way home ) . a battery saver mode is also good or get a 12 volt plug .if you are after a mounted one don't forget the aierial and found out if it needs any extras to run also a look back will find that someone did a chat board on this . hope this helps
Anzac