Screen flickering is normally due to low battery voltage. The battery voltage is not measured but a coulomb counter is used to measure energy used. When battery is put in it asks is it a new one so it can start at the correct point. If this is not done and a used battery is fitted and the new battery fitted is selected then the green battery indicator bars at the top of the display will not display the state of the battery correctly as in this case it will be showing the battery state is ok (3 bars) when in fact it could be near complete discharge and the screen will flicker and the battery indicator will show that the battery is ok. The correct battery must be used not a D cell as this is lower voltage (1.5V) and the screen will flicker. The battery nominal voltage with the correct type of battery fitted (Tadiran) is 3.6V.
The batteries fitted into the UT5000 must be of the correct type for the unit to operate correctly and that type is shown below:-
Tadiran Battery distributors
Tadiran Battery part code
North America: TL5930