Yes, it could be the
battery. Has it been out in the sun enough to be charged? Could the little
solar panel be covered? You can replace the internal
battery, but it requires that you take the unit apart.
I had an old Tacktick wind stop transmitting directional data recently. Speed
transducer (spinny cups) was occasionally seizing as well. Sent the unit and display to
Raymarine and they sent me what appears to be a new package for about 1/2
price of new.
Why go fast, when you can go slow