T7406E shutting down

[ironhorse17]

I have installed a slightly used one year old T7406 E on a new site phone works good, after an hour phone displays shutting down no warning for low battery; indicator shows full charge; what does shutting down mean, low battery, lost communication with base, port lost contact with base?

 

[cook1082]

Sounds like a bad battery, even though it does not say low.