Wow, go away for a few days and look what you get. Lots of great information - thanks! So heres the update. I took the big dive and broke open the Garmin 235. Easy to do, 12 screws and the back is open. You have to be careful since the back is still teathered to the cover by the connectors. Sure enough, the battery has soldered on legs that need to be disconnected from the PC board to replace. I have a couple of blurry pictures if anyone is interested.
So have I replaced the battery yet? No, because there's more to the story. I've gotten quite the lesson in history regarding Garmin and their supplier for the SD chart cards 10 years ago. The short story is that Garmin no longer supports this unit or the SD card charts. That leaves me with a working GPS / Sounder that does not have a SD chart of my area i.e. unit gives me my location but without the map overlay. I could buy a card off ebay but the information is at least 10 years old. I decided not to pursue fixing the Garmin 235 any longer. I may turn it in to a portable side scan sonar to see what's under the dock when we're out back fishing.
I read Gradyfish22's comments in thread titled "electronics update" (excellent information by the way) and was trying to decide if I wanted to invest the money in an entire system or get an all in one unit. The larger displays are awesome but I'm not ready to do a major overhaul of the helm station and I'm not ready to spend that much money. In the end, I decided on a Garmin 545s for a couple of reasons. Obviously, cost was one factor, ease of installation another and the fact that it will work with my current through hull transducer sealed the deal. I have already ordered the unit and the appropriate G2 vision card for my area (South Florida) and even sprung for the XM antenna so I can sign up for the weather service. Now I just need to practice patience while I wait on UPS.
I appreciate all the responses to my initial query and want to thank to all who offered help or guidance.
