How do I measure the charge level of the 8000mAh power bank with the NodeMCU?

Hi,

I have connected myself a NodeMCU with sensors to a local domoticz, it sends me cool data, powered by an 8000mAh power bank,
Is there any way to measure the charge level of this power bank? Probably through this usb mic input is 5V, and then before the ESP probably some kind of stabiliser (I'm a weak electronics guy). I would like domoticz to send me a text message when the charge (voltage?) level drops to a low level.

regards.