Power! A lot of cosplayers need it, love it, use it. This is a battery box for a 26650 3.7v 6,000mA lithium Ion battery, a very compact, high energy battery. It has a tiny rocker switch for power and space large enough to fit a 5W resistor or tiny constant current limiter. The battery provided power for 50 x 10,000mcd brilliant white LEDs for about 8 hours.

The LEDs were arranged in a parallel configuration, the resistor was calculated for the voltage and current of the LEDs used for this project, you will need to adjust the resistor based upon your LEDs power requirements. If you use a constant current limiter you can calculate the maximum number of LEDs based upon it's current rating.

Component list for what is shown is as follows:

Lithium ion batteries & charger - $26.88
100 pieces 120 degree 10,000mcd white LEDs - $5.65
20 gauge hookup wire - $4.97
1/4" copper tape - $12.30
1Ω 5W Sandstone resistor - $0.36
SPST Micro toggle switch - $1.17

Cost for the battery box (excluding battery) and lighting was about $20, some of the list items are more than what is needed for this project. Other various items included a spare 2.1mm barrel jack and plug set, bare 24 gauge copper wire, a tie wrap and heat shrink. The copper tape is for the battery contacts, I recommend soldering the pigtails that run to the switch compartment to the copper tape before removing the adhesive tape and installing. The wiring diagram is extremely simple, we used bare copper wire to solder the LEDs together. Spacing was adjusted based upon position and location within the headdress and costume.

NOTE: Be careful to insulate the wires after you have the desired shape to your wiring harness, if the wires short out it can heat up the copper wire very quickly. Lithium batteries can be very hazardous if shorted out, do a visual inspection before you connect the battery to your wiring harness.

The pictures are from my daughter's Devil Mercy costume she wore to Blizzcon 2016. While I was 'consulted' for the battery box, she did all of the soldering and wiring for the costume.