Well first make sure you're using the charger it came with. Any other charger may have issues.
You can always go to your battery settings under Settings > More > Battery to see what's causing it.
Have you installed any new apps recently? Maybe something yoi installed or updated it causing it. You could test this by uninstalling any apps you recently added.
Another trick, try charging the phone while it's off. If you see the same pattern, charging slowly until unplugged then quickly after being plugged in again, then it might be a problem with your battery. If it charges quickly every time it's off, then it's a problem with one of your apps.
Also, not to sound insulting, but by off I mean powered off entirely, not just sleeping.
Posted via Android Central App