What I would recommend is go to Lowe's and buy a rechargeable spotlight. It has a small, removable, sealed battery that works for a fishfinder. That's what I did. The battery weighs about 2lbs and the whole spotlight costs about $10. You can get one at Bass Pro Shops or any of the boating stores but those cost twice as much. When I put 12V running lights on my yak I got a second battery because the light would drag the voltage down and the fishfinder cuts off. With just the fish finder on one battery it has lasted me for 6 hours of fishing and is probably good for longer (haven't been out longer than that with it).