6310 series definitely the best phone for reliability and durability. Have never had a flat battery (it just needs about 30 minutes in the car kit and endurance > 7 days. I dropped mine off a boat in Loch Lomond a few years ago (luckily in shallow water). I found it 36 hours later. I drained the water out and dried it out with a hairdrier, the phone has worked perfectly ever since.