Thank you for your reply and additional information.
First of all, I need to say that you did a great job. You already tried all available online troubleshooting steps.
Battery should last minimum 2 years. After 2 years the signs of capacity reduction can appear (won't charge, low battery level etc.).
Problem on your Tab can be bad battery or defective charging port. Because defective port is the main problem in 95% it's not a good idea to replace the battery without testing the Tab.
The best option in this case (hardware problem or bad battery) will be to contact directly Samsung at 0330 SAMSUNG (726 7864) (Monday - Saturday | 9am to 6pm) to arrange repair.
If you want to replace the battery by yourself please check the Ebay offers for the battery replacement - click here
. Step by step instruction how to replace battery - click here
Sorry I could not be of any more assistance, but there is a hardware issue that can't be resolved online and you already tried all available troubleshooting steps.
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that will result in a permanent negative feedback on my record (very damaging for me), use the link below to request refund (your deposit will be refunded) - click here
If you need more information please don't hesitate to ask. I'll be happy to help with any follow up questions.