I had a similar issue: how to raise a hydraulic hatch on a 340 Sundancer, when no 12 volt power was going to the lift motor. I wrote Searay who then had a rep mech. from Marine Max explain the following procedure. He said to to use a 12 volt plug, that plugs into the 12 volt auxiliary, that looks like like a cigarette lighter receptacle. The type you plug into for auxiliary 12 volt power, such as for a portable gps or radio, hand held spotlight, etc. The leads are then connected to a fully charged 12 volt battery (one you removed from your vessel), of course positive to positive and negative to negative. I ordered the plug in adapter with 3ft leads from Amazon, that have rings on the ends to connect to the battery terminals. I had to use a round file to make the holes in the rings slightly larger, so they would fit over the threaded post and could be held down with the nut or wing nut. I believe the gauge wire for my model vessel, I selected, was 16 AWG. I did notice that the opening and closing made the wires slightly warm. So for my application, I was glad to have the heavier gauge, as compared to other assemblies offered for sale on Amazon. The actual part I ordered was a Carviya 12v heavy duty 16 awg 15A 20A male plug cigarette lighter, price 7.99. You can look it up that explains pictorially what I wrote above. Also, I used the 15 amp fuse being the same on the vessels breaker panel. On my vessel the 12 volt receptacle is wired directly to the breaker panel, under the helm. That panel is also where the hatch motor wire is connected, so it is receiving the back feed from the receptacle. Thus, power is transmitted to the source. When it comes time to open the hatch to install the batteries, it is the same procedure. There should be an extensive post that I wrote about this procedure earlier, and several suggestions I received from our community.