Hi @Toni9, sorry to hear about this. 
Is there any change if you charge the device when it's powered off, or is still only charging to 50%? If there is no change even when the device is powered off, remove the back cover and you have a small OFF button that you can press and hold for 10-15 seconds with the tip of a pen. Charge the device for 5-6 hours while it's still powered off and see if it reaches 100%.
Let me know if that helps!
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