I have the same issue and changed the battery twice but I don't think it's a battery issue. What I have started doing is turn the fob off every time I stop and leave the bike. I turn it onto "green" when I'm sat on the bike and ready to start.
I have not had the out-of-range warning since I do this procedure. If you walk more than about 6ft away when the ignition is on and no engine running, it will be out of range, and it doesn't re-set when you come back in range. You need to turn off and start again. Bit frustrating but I don't think it's an actual malfunction, just not very user friendly. Hope this helps.