*edit*
Check post below.
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OK, so that has a BMS. How long has it been since your shorted it? If it's more than half an hour you an assume intervention is needed.
Do you have a low current 12v supply, say an amp or so? An old ADSL modem / router power supply would be OK. If you do, connect that across the battery, taking care to ensure + from the power supply goes to + on the battery, and likewise for the - and - terminal. At the same time connect your multimeter so you can see the voltage on the terminals of the battery, then with your 5th hand turn the 12v power supply on, make note of the voltage, then turn the power supply off.
Do not use another battery to do this. We need to ensure that what ever we supply power to the battery is not capable of much current.
Did the voltage read by the meter increase, if so, to what?