Battery not fully charging at 100%

This happens every time I use the Z10 to the point that it shuts down on its own. After that, I charged it. The amber light begins to blink slowly. After 5-10 minutes, the Z10 turns on itself (normal). I leave it charging and after 3 hours, I know that it should have been fully charged. But at this time, charging stops at 96 or 98% and you know that the Z10 thinks it's full because of the battery icon with small lines on it and my battery app says 96 or 98% full. On the other hand, if the Z10 turned itself on then I turned it off, you will see the amber light slowly blinking meaning it's charging, and after 3 hours expecting a steady green light which means it's fully charged but no, all that you'll see is the slow-blinking amber light that takes forever (I assume that this means the Z10 never flashes the green light when it doesn't detect a 100% charge).

This issue doesn't happen if I don't drain the Z10. If I charged it before it shuts down, I will see a 100% battery full indication and the steady green light if the device is off.

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