The darned thing was not holding a charge. She's old but still sounds nice. No need to replace if $10 battery could fix!
Success! The unit functions as new.
Finding a replacement battery can be a challenge. After one bad purchase that did not fit the case, I saw another comment from a user that found a perfect match in terms of size. The issue was that battery was in Europe. I found it via Amazon in the US and A:
FLOUREON 7.4V 1000mAh Lipo Battery Pack 2S 20C RC Battery with JST Plug (Grade A cells)
Unlike the OEM battery, this one has two sets of plugs. To use this battery to replace JBL:
1) Peel the plastic wrapper from the battery. Careful not to cut into the battery!
2) Cut the 2-wire plug off at the points they are soldered onto the replacement battery.
3) Cut the plug off of the replacement battery at the plug end - leaving plenty of wire.
4) Unwrap the original battery and cut the plug and wires as close to the top of the battery as possible. Again, looking for the plug with plenty of wire to work with.
5) Splice the two together. Start with red to red. Then find the negative on the replacement battery and splice that to the black on the original plug. Negative is usually the left terminal when looking at the battery standing vertically. Then the remaining black wire (which was soldered across the battery) goes to the blue wire on the original plug.