Quantity   Component name
1 × Raspberry Pi 4 Any RPi will be fine, but you'll need to swap out USB cables to fit your requirements.
1 × 3.7v LiPo (Lithium Polymer) battery I'm using an 8800mAh one from Pimoroni. Be careful with LiPo batteries! I recommend you use one with discharge and short-circuit protection.
1 × MP2636 Power Booster & Charger Module This li'l friend converts 3.7v into 5v to power the RPi, outputs a hefty 2A, and charges a LiPo battery! You can also use the Adafruit Powerboost 1000C or any of its knock-offs (but the Powerboost only outputs 1A, so it may have some trouble with the RPi 4).
1 × Super Cute USB power switch Get it on Tindie! https://www.tindie.com/products/8086net/usb-power-switch/ The only problem with the MP2636 is that it doesn't have headers, so you can't attach a switch to it. This simple USB switch sits between the booster and the RPi, and is operated with a toggle switch.
1 × Toggle/rocker switch Any kind will do! This allows you to connect the RPi to the MP2636 with a flick of a switch.