Diagnosis
A loose or corroded connection between the main body and the battery pack is causing voltage fluctuations that corrupt the display driver.
How to Fix It
Reseat and clean the main power connection. Step sequence: 1. Power off the device. 2. Remove the battery pack. 3. Inspect the eight metal contact pads on the vacuum body and the battery. Clean them with a dry microfiber cloth. 4. Firmly reinsert the battery until it clicks twice. Power on to test.
If That Didn't Work
The problem may be internal to the display ribbon cable. This requires professional service. Contact Tineco support.
Heads Up
Do not store the vacuum in a damp location like a wet laundry room. Persistent humidity corrodes electrical contacts.