The battery will live in the opposite pocket as the joystick. This makes the hat feel more balanced, and makes it easy to remove and change or charge the battery.
The simplest and safest option for power is using four AA batteries in this battery holder. When using alkaline batteries, the output will be around 6v. This is perfect for our project.
Add a couple feet of wire so the battery holder reaches one of the hat pockets. This battery holder doesn’t include a JST plug…you can either add one from the shop, or solder the + and – wires directly to Circuit Playground’s VBATT and GND pins.
You should be able to use either alkaline or rechargeable batteries in this holder, but keep in mind that rechargeables have a slightly lower voltage so if your servos don't respond as well, try switching to alkaline.
For those who want a little more battery life without adding to our planet's overwhelming landfill problem, Adafruit sells these fabulous Lithium Polymer batteries. The 2500 mAh battery will give you 3.7+ volts for hours, and runs this project very nicely. The voltage is a little lower than recommended for servos, but we've found that it works just fine.
These batteries come with a protection circuit onboard, so you can run them down willy-nilly and recharge them hundreds of times, without worrying about the voltage dropping too low for recharging. They're smaller and lighter than AA batteries and easier to hide in costumes. Be sure to get a charger, and if you want to take your project to a weeklong festival with no power plugs, be sure to get a few batteries or get a AA holder as backup -- you can't find these at the corner store.
They don't have an on/off switch included, so you'll want to add one.
There are dangers that come with LiPoly batteries. If the batteries get punctured or torn, or if they get wet, there's a chance they can catch fire. You may not want to use LiPoly if you're making this project for a little girl, or for anyone who's likely to spill on / drop / engage in fisticuffs in this costume.
Cut the female end off the power switch and splice in about 3 feet of wire, enough to reach the Circuit Playground / horn assembly.
Cut a small hole in the pocket lining and thread the switch and wires through, leaving the male connector accessible to plug in your LiPoly battery.
Thread the female end inside the lining up to the Circuit Playground.
If you're using a LiPoly battery you can plug it directly into the other end of the battery extension cable. If you're using the AA option, cut off the male connector and connect the battery holder directly to the extension cable wires -- red to red and black to black.