What are you plugging the usb power cord into and are you using a good quality usb cord. Says it needs 5v 2a input power.
On the website it says “when a over discharged IMR is inserted the screen will display EE EE, in this case long press V for restoration mode”.
Since you didn’t say it was displaying EE EE and showing 0v, I’m just guessing that its not plugged in to a appropriate power source or maybe a cheap usb cord.
Some cords will not do more than 1 amp even when plug into a 2 amp capable power source. I’m guessing the resistance is to high and the device steps down the charging to 1 amp thinking the power source isn’t capable of 2 amps. Just my guess, but its not the first time I have seen cheap usb power cords only allow 1 amp output.