Found this info re your battery problem here on this link
This is taken from a post in the above link.
"If you cant install the new BIOS because your battery is less than 30% (what was lenovo thinking!) there is a solution. Download the new BIOS, download WinRar, use it to extract the files from the installation package, open Platform.ini. Search for BatteryBound=30, change that to 2 or 1. Save and run H2OFFT-Wx64.exe This will install the new BIOS."
Here is a link to the latest BIOS updates - I think it is for your Tab, you'd better double check me.
The 1st link above is p8 - you may wish to read forward on p9 regarding calibration of your battery.
It seems that you are not alone with your problem