hm, you know what is wierd... With my old graph (Lowrance X-91) my battery only lasted about 2 years and then it was like you said, the battery would die after 3/4 of a day or 1/2 a day.

With my new graph (Lowrance LCX-17M) I got a new battery like that and it has lasted much longer and it still powers it all day no problem. I don't know why a larger graph would last longer but it seems like there's some variation in how much electricity these graphs draw.

Isn't have a boat fun :) It seems like there is always something to fix.