Watch does not turn on after long period of disuse - and it's a $2 cable

Wow, glad you got it sorted! Sorry to hear about the cable - does it look ok?

A few people have had issues if they leave the cable plugged in and their USB power supply doesn't have current limiting. In that case the cable can pull onto metal surfaces and can short itself out.

But if it's just broken I can get a new one in the post to you.

... also maybe a month of disuse shouldn't cause a turned off watch to have zero charge?

New firmwares should do a better job of saving power. It's not ideal, but like a lot of devices now there's not a global 'off' switch - everything is still connected to power, it's just put into a low power mode when the watch turns off.

Also, if you turn off from the Bangle settings menu it'll go into a much lower power mode than if you use the Bootloader hold 2 buttons method (which is kindof a last-resort way to turn it off - the bootloader doesn't have the resources to communicate with all watch peripherals to turn them off properly).