How do I replace battery? - Jabra BT350 Bluetooth Headset Headset

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).

So for pictures of disassembly, and of the interior including the battery, see the instructables link above. No pictures of actually jumpstarting, but here's a description that I hope is clear enough to be useful.

For me, I didn't need a multimeter to determine the battery polarity: the + and - were marked right on the top of the battery, about 8mm from the edge of the battery that attaches to the motherboard. Look for it, it's small, but it's there.

As for the jumpstarting setup, I simply used some scotch tape to put 2 1.5v AA batteries together in-line, attached a wire (actually, 2 xmas tree ornament hooks bent straight) to each end (also with scotch tape), and then touched the wire on the + end of the AA battery contraption to the + lead on the Jabra battery and the - end similarly. (+1 to asweber411 for this idea) Held for about 30 seconds, got tired of holding the whole bloody thing (it's small, my hands are shaky and my eyes are not great) but even 30 seconds was enough - this worked like a CHARM! I was totally skeptical at first. Props to Ruprik for this fix, it recovered a 2-year dead Jabra BT350 today and made me a very happy camper.

Important tip, don't reassemble the whole thing before trying to plug in the charger to see if the red light will stay lit after this procedure. If you have to do it 2 or 3 times (or, if like me you're shaky and not 100% sure you had good contact) it will save you from a disassemble/reassemble cycle.)

This worked perfect.
I was a little confused and had the battery only on the + Bluetooth + terminal.that didn't work. I re configured my two double aa's batteries taped together with two small pieces of wire.hardest part so far was holding the wires on both.
I only held mine on for ten or so seconds.
my foil got trashed when I was taking it off it all stuck to the device. I think im going to hit it with a sharpie or cut some foil and glue the faceplate back on.
I have no training in this field. Thank you your instructions are very good.

Crazy thought do you think it would be a similar solution to jump start a dead laptop battery? don't try this unless one the gurus gives us an answer. it would be very dangerous to try it without their thoughts on the matter.