Yo know what the problem is with power switches? They're bulky, especially thickness-wise. And all of the ones I have in my junk box are way too large. The best solution to this problem is an electronic power switch like this one. And you get the added capability of having the Pi shut it's own power off.

While pondering this problem, I realised that the electronic switch is just a pass MOSFET, some electronics, and push-button switches. And the battery protection module is a pass MOSFET (actually back-to-back MOSFETs) and some electronics. Maybe I could add push-button switches and get the same functionality?

I searched for images of battery protection modules on the Internet. It seems the DW01 chip is pretty common. So I took a look at it's data sheet: it disconnects the load if it's CS pin rises more than 150mV above ground and reconnects it if it's lower than 150mV. So, connecting CS and V+ with a switch will disconnect the load, and CS will stay at V+ once the switch is released. To connect the load, momentarily apply power to the load with a switch: this will lower the CS pin to ground potential and turn on the MOSFETs, and they will stay on once the switch is released. There, I just made an electronic power switch by adding two push-buttons to the battery protection module!

Here is the unmodified protection module:

Here is the protection module with added switches: