The unit was returned and an evaluation wsa conducted.
Upon visual inspection it appears that a thermal event occurred.
It is not possible to determine the exact sequence of events that led to the thermal event.
However, there is evidence that a short occured in the lower battery pack between the cells and the printed circuit control board (pcb).
There was a blackening on the top of the lower battery pack and its printed circuit board (pcb).
Cells 2 and 3 appear to have been involved in the thermal event, likely by supplying energy into a fault in the board.
Additionally there was a slight melting of the handset plastic enclosure.
This concludes the investigation.
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