I had the same problem... the battery is part # 501235 and is 3.7v 150 mah (yes, it's tiny). Searching for this on the web yields such a part at various places but not any retail options that I could find.
I took it apart per the instructions at instructables.com (above) and then jump-started the battery using a maglight penlight. Sometimes rechargeable batteries get "stuck" on empty when they drain down to absolute zero and have trouble accepting any charge... To jumpstart it, do this:
Get a Maglight AAA or AA penlight (2 cell) and unscrew the end as if you were going to replace the light bulb. The bare bulb must be on when the reflector is removed (or, perhaps the batteries are dead).
Remove the bulb.
Obtain two short (1") pieces of bare 22-26AWG wire and insert them into the holes where the bulb wires were previously inserted.
Using a multimeter, determine which wire is positive and which is negative
Align the + terminal of the rechargeable battery in the Jabra with the positive wire identified on the flashlight - do the same with the negative terminal. Hold the flashlight on the battery for a minute or so to allow some of the current from the light to slightly charge the jabra battery.
Before putting the Jabra back together, try the AC or USB power cord - you should now get a solid red light if it is charging.
If not, try to "jump" it again for another minute or two or three.
If this doesn't work, the battery is probably totally shot - maybe you'll have better luck finding a replacement than I did.
The Maglight isn't necessary, but it is a simple way to obtain the 3.0v DC power source. You could use a similar power source to obtain the same effect (probably 2.7-3.7v DC is best).
on Jan 29, 2015