This might help. The Terrova takes a 2450 lithium battery BUT not all batteries are created equal. I had intermittent problems too, swapped new batteries, removed battery/place right back in on the water to make it work, etc. Then after some research, I got the 2450N
. It is a little complicated but read this
. I'd suggest reading post 18 and click the OPs 'here' for a full description.
I got my 'N' at Radio Shack.