Very unfortunate that nobody seems to warn the buyers that the bms they build into the battery will ruin the battery if stored for very long. They may have stated that the battery should be charged if stored long, but never said why. This knowledge will become common some day, but at the price of lots of people learning it the hard way as you just did.
Very difficult to dissasemble those metal boxed batteries enough to diagnose them too. Like lots of modern stuff, "no user servicable parts inside". Could have been before they went crazy with the hot glue.
At this point though, you have two options, trash can or have a go at finding the bms and the wires to the battery cells buried in all that glue. Chances are, replacemet cells will be difficult to obtain, your time is worth money, etc. Unless you dig taking stuff apart like we do, just getting out the credit card and buying a new pack might be your best bet.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE
Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum
See battery technology section, FAQ thread at the top of the page for lipo noob info.