I've just remembered - long before these rechargable n-million-candle spotlights came onto the market, there was one UK company who made a vehicle hand-held spotlight which was, for all the world, nothing more than a rectangular car spotlight/driving light (the kind you often see hanging down under front bumpers). It had a handle on the back, and clipped into a custom holder when not in use - otherwise it was a bog-standard car part. Had a cigarette lighter connection on a six-foot lead. No batteries, so was extremely lightweight. Don't think they make them anymore. I bought one last year at a boot sale for a quid, but haven't used it yet, so can't comment on the beamwidth.
I have a club boat that is used for "night patrols" and I have fitted a standard marine halogen spotlight (all rubber with coily coil lead) that plugs into the ships supply via a deck plug and it's proved more than adequate.
Last year I bought a 500,000 candella 12v rechargable one from Wickes. I know it's not what you asked about but I felt it was worth a mention as it only cost £3.49
Agree on the Aqua Signal 12v model which if wired to a cockpit 12v socket makes for an excellent set up. Found it worked perfectly for those night arrivals at Newtown Creek!!