So I'll probably be picking up some sort of depth finder for my little Zodiac (or Jon boat whenever I purchase it).  Primarily I run on just a trolling motor hooked into a 12v deep cycle due to electric only restrictions.  I've seen the clamp on fish finders that transom mount and run on a few AAA batteries.  My question really would be, if I was to pick up a standard depth sounder would I need a second 12v battery to run it or would just a single work.  The clamp on style really limits the options to what electronics you can buy.

If you run on one battery. The only problem you may have is the trolling motor causing interference with the depth finder. If you can live with that you'll be OK.

most likely you will be fine with them on the same battery.Make certain you use an inline fuse that matches the sonars specs and have good connections,and also make sure that the transducer (which should have a crease or line on it) is parallel to what would be the ground if the boat is floating on water and not how it sits on the ground or a trailer.You may know that  already.I use 1 battery to crank only and another runs my TM,livewell,lights,2 sonars(a hbird and an eagle)and bilge.I can use the TM + the 2 sonars without issue.I hope you enjoy your new boat(whichever kind you get)as well as your sonar,and read the sonar articles on this site,if you haven't already.They've helped me greatly.

catch em' all :)release em all

i run my 45# trolling motor and garmin fish finder both on 1 12v battery and it works fine.  i have never had a single problem running both on the same battery.

Thanks guys. I had a feeling that was a silly question. I've got 5 batteries on my large boat, but I was just dumbfounded about using the TM and a sounder on a single battery.  I was mostly concerned about interference, but that doesn't seem to be much of an issue from what I've read.  The boat is mostly for playing around in the backyard, so I've got a newish toy to play with for now.