Shearwater's Teric doesn't have a user replaceable battery. Shearwater wants you to take it to a dealer who will then mail the thing to shearwater for $100.#shearwaterTeric
I think the Shearwater Perdix ai is probably the closest computer to meeting all of the criteria set by @Andrew Dawson . If he could forego the replaceable battery then the Teric fits the bill nicely. If he can forego the "watch style" requirement then the best fit is Perdix.
Personally, I wouldn't consider an Oceanic, Aqualung, or or Deep6 unless your budget is just too tight to spend any more. Those are all okay to get you by until you can afford something better... but that's as far as I'd go.