I have a Garmin Etrex Venture Cx handheld and it is excellent. I've been smallcraft boating again for the past few years after a 15yr gap and it's the thing that's impresed me most in the advance of tech devices.
Mine is small but has a colour screen and full Bluechart mapping. To see detail mapping on something that fits in your pocket never ceases to amaze.
It's also useful when arriving home to upload all track data for display on the PC.
My Etrex is waterproof (but not floating) and has been completely reliable despite several years of bumping and splashing about on holiday around Scotland.
It takes ordinary AA batteries and a pair will last a long day out with lots of looking at the screen (screen times out after a selectable period). I'd far rather this battery arrangement as a couple of spare batteries are easily stored in the pocket. I had looked at upgrading to a similar unit with larger screen but that had a fixed internal rechargeable battery which would have rendered the unit useless once it went flat out on the water.