Galaxy Tab 2 10.1: Battery indicator acting weird

[Arievanl]

I have a one and a half year old Samsung Tab 2 10.1, stock android 4.2.2
Last week suddenly the battery indicator started to behave strange. After charging it indicates 100%. When I disconnect the charger and start working the indicator stays on 100%
When I put the tablet on stand-by for one or two hours and switch it on again, the level has gone down till sometimes 2%. I can ignore the message to connect to charger and after some minutes of working the battery level starts to go up again. The battery stats show then a straight line down till 2% and from the beginning I start using the tablet it starts to go up again. Again, this happens when I'm not plugged in. By the way, when I look at the battery stats in the first period of working, it has a horizontal 100% line, later this has changed into a straight line down.
The list of battery usage per app does not show something strange, except that the screen is using most power, even when it's off most of the time.
Does anyone has any idea what causes this problem and what to do about it?
Thanks.

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[Golden Bulls]

My S 10.1 tablet would have been two in March 2015. It crapped out with the same battery issues you have. I can only guess it needs a new battery ....what a piece of s_ _ _.:-\