Pretty simple speaker, very good battery life, build in bluetooth.

It's assembled with

laser cut 4mm plywood (31cm x 8cm x 8cm)
4x 2" drivers from small notebook speakers (EARISE AL-101, they are surprisingly good)
2x 18650 3000mah
TP4056 charger with cell protection
bluetooth module
3.5mm female jack
basic on/off switch
2x 3W*2 class D amplifier (pam8403)
optional: 2x step-up(boost) voltage converter

Step 1: Box

The plywood was cut with "tooth" shapes so it's easier to glue. Heat from the laser bend it a litte.

Apply glue to every panel except top or back and put it together

Step 2: Back Panel..

I forgot about holes on back panel and had to improvise a little. Drill and wood file ftw.

Step 3: Back Panel

Hot glued switch, jack, TP4056 charger (I added a heatsink), pay attention to that little hole next to it and hot glue on charger LEDs, it will lead light to this hole and indicate if battery is charged or not :).

Hole one the left is on/off switch of BT module covered with wood.

Step 4: Wiring

I used a cheap bluetooth module with on/off button and jack output, so you can use it as bluetooth speaker or just as aux speaker when BT is off.

If you want a better module i recommend CSR6035/CSR6045 module (~7$ on aliexpress) but you have to figure the wiring on your own ;). http://www.aliexpress.com/item/Bluetooth-4-0-Stere...

The PAM8403 amplifier is small, powerful,power efficent... and costs nothing

http://www.aliexpress.com/item/10PCS-PAM8403-Super...

Charger - it's important to use TP4056 WITH cell protection, so they are safe from over discharge

http://www.aliexpress.com/item/2pcs-Lithium-Batter...

Capacitors that I used may be too big/useless but it's good to have one than not having it at all :D.

optional: to achieve better sound quality on higher volumes put an voltage converter (from 3.0-4.2 to. 5.0v-5.5v) before amplifier (one converter for one amp), most of the bluetooth modules uses 3-4.2v so leave it straight to battery. And you should use batteries with bigger capacity/more of batteries connected in-parallel.

(this one is nice, with 2A current) http://www.aliexpress.com/item/2pc-DC-Boost-conver...