My Navman nuvi 50 died yesterday. It was about 6 years old. The battery originally had a very short attention span, about four hours. I then used the car lighter outlet for the next four years to power the unit. Given the OEM support listed, it would be unrealistic to expect a battery life of more the two years, about the length of the warranty. I had not used it for twelve months and when I went to operate it, it refused to fire up, so today I bought a Garmin nuvi 67, as I was happy with the nuvi 50. (R.I.P.)
Having also previously owned a Tom Tom and a Navman, my preference is for the Garmin for map updates and ease of use, but I believe most GPS units are throwaway after two or three years and therefore may not warrant the expense of paying a premium price for a more expensive unit.
Update to follow after I have used the nuvi 65 for a while