Gate worked the same and leccy was switched on when I got "weathered" in Cardiff a year or two ago.
There were a load of fishing boats there but they snook me in and made us most welcome.
I understand they are now up the Taff?
Up the Taff, sounds like an Eric Sykes film!
Down side of that old graving dock is not a very pretty outlook, but an easy walk to CYC for a pint!
The pontoons there are clear of the fishing boats as they live up the Ely now. Last I knew the gate lock is perminently left open. A simple call to the lads in the barrage should be able to answer your Q's about that and the electricity. Might be worthwhile looking at the HA website for any info regards berthing in the bay.
One thing to be aware of is the the part of the pontoon right at the entrance and a good 70ft along is a water taxi berth that is used by Aquabus and Cardiff Cruises so best steer clear to avoid hassle. The dock is a little out the way but as previously said, a mere jaunt down the road to CYT, who are very welcoming.
i used the pontoons about 6 weeks ago. Gate worked fine but the electric at power service bollard was dead. All mcbs and rcds on so think it was isolated further back.