Sorry I left that out, new wires new furnace, new heat pump. Everything new.
I took the batteries out of the stat to see if it would work on the furnace 24V power. It didn't.
Located and attached a wire to the common 24V lug on the transformer and then used the "extra" blue wire between the furnace and the stat attaching it to the C stat terminal. Checked voltage at the stat between C and R (24V) and replugged w/o batteries. Display now works w/o batteries.
Added benefit - there is a bright red lamp when operating on emergency power that have never seen before. Maybe does not glow when on battery only.
So it seems for two years it has been operating on battery only.
Have to wait and see if it solves the frozen screen problem. . .
Keeping fingers crossed.
Thanks for your help.