For many years I did not have a fishing boat, and still don't as mine is being built now. My biggest complaint was when I would get on a friends boat, or rent a boat, the electronics were typically nothing more than a glorified depth finder. In doing my research, I found that the typical Humminbird portable units weren't really that great for what I wanted. I ended up purchasing a 787c2i and portable qudrabeam transducer.
To make the whole thing portable, besides the portable transducer, I mounted the unit inside a pistol case on a piece of plywood. The foam from the gun case was utilized to cushion the unit during transport. To lower the footprint of the case while in use I made the hinges of the gun case removable.
As for power the plan was two fold. First, I did some math concerning the use of a 12Ah battery. Ah stands for Amp Hour. To figure out the amp hour you take the Ah and divide by 20 hours. Example: a 12Ah battery is 12/20 = 0.6 amps. This means that a 12Ah battery can maintain 0.6 amps for 20 hours. The 787c2i draws 560mA or 0.56 amps. So a 12Ah battery would run this unit for about 20 hours. This will also be supplemented with a 12 volt hook-up that has a cigarette lighter adapter and alligator clamps allowing hook-up to any 12V source. The batteries are small 4"H x 6"L X 3.7"W. I believe Humminbird actually sells these batteris now, they didn't when I set this unit up. This setup works like a champ. I've taken it to Canada but typically use it on friends boats. My new ride is coming equipped with a 997. Once the boat is delivered, I will set this unit up on the bow of the boat with a quick disconnect. I'll get photos of that install as well. Here is the portable unit as it stands.