My wireless headphones broke today, I dismantled them and took out the battery and circuit board. Both of witch still works. I will dispose of the battery, since I'm a bit scared of it. The battery was a 3.7V Li-ion Polymer with 670mAh (2.48Wh).

I would like to power the board with two AA batteries, but I don't think they would be able to handle it. So I was thinking of a 9v, but I'm not sure how to properly install it. The only way I can think of is to use a resistor on the wire before the 9v and the board, but is it that easy?

 

Try two AAA batteries.