Battery or not as issue

[Rich99999]

Hi guy's, I have a vtbox 250 and it has stopped working. When I last put it down the battery was reading 40%. I went to pick it up again and have a vape and the battery indicator was at 0% and the screen was very dim. I have tried to charge it but nothing.... I have plugged it in to escribe and 2 cells are at 3.37v and one cell is at 2.20v. I initially thought the battery was dead, but I've since tried another battery which I know is good and it's exactly the same. When the usb is plugged in the screen comes on but only very faintly. Any ideas what the issue could be? not very happy as it's only 2 months old and the vender I bought it from isn't interested.. Thanks in advance for any suggestions