Onyx Boox conducts strict quality control over the raw materials before production. We have forwarded this to our relative colleagues, and they suspect that it may be caused by misuse of the charger or USB cable when charged the device before. BTW, users are suggested to use the 5V 2.4A charger to charge the device for a better battery life. Or the battery was squeezed by other parts of the device during dismantling.
Apologize again for any inconvenience that may cause. Onyx Boox would give serious consideration to selling batteries or other accessories separately to customers. However, as we have discussed before, the e-ink screen is so fragile that it would be broken during dismantling and repairing by customers themselves. What is more, it is not easy to ship the lithium batteries internationally, especially to some countries. Hope you could understand that.