I have a Waeco, which lasts about 12 mins, and which sucks up water as well. 122v battery ( thanks, I mean 12v /forums/images/graemlins/blush.gif) recharges in about 2 hours from empty.
You can get a car version of the dustbuster in halfords which plugs into a cigarette lighter type plug. Will go for a fair while on your domestic batteries! Never going to be as powerful as a 240v hoover, but their adequet for quick clean ups.
Funny mentioning Halfords ... just a short while ago was yahoo'g with a mate and we both commented that Halfords is no longer the Car Spares place it used to be ... now full of Sat Nav ... Camping gear ... and bikes !
I have a B&D 12 volt plug in one. Works well especially when combined with stiff brush. Also came with extension hose etc that has allowed use with a vaccum scrapper. Not sure on battery consumption but it does not take long to vacum inside of boat after a weekend.
Aldi had a 12v (ciggy lighter powered) one on offer a few weeks back, we bought one and it works fairly well, it was £9.99 may be more now but worth checking.
I use a Ryobi 18v one. Wet & dry and the same battery also runs a load of power tools (called one+ range or something).
On the boat I have a lantern, torch, drill and vacuum. I only have one battery on the boat (but others at home) so it is fine as long as I dont need to hoover in the dark!!!