I haven't used the EZReader for months, and the battery was depleted.
I plugged it into the wall and it started beeping.

ALso the light switches from red, orange to green (orange = red and green together).

I managed to plug it in and boot it; but wonder if the changing R/O/G colors and beeping have anything to do with a bad battery?
I think I've had that problem with my BeBooks. I just left them on the charger overnight and things seem to have sorted themselves out without further problems.
That is the 'Very low Battery' warning.
Charge (using the supplied charger. Using a USB port could take a full day) for at least 14Hrs. Best wait for the 'Fully Charged' symbol (a power plug).
Left it charging for like 2 days, completely forgot about it;
It does seem like it recharged the battery, though I don't know how long the batt will hold.
I've currently got 4 ebook readers, and can barely find time to read with one.
Bad investment?
Perhaps...
After what seems like 4 years, my ereader still boots up, but with empty battery sign.
I plug it in USB port, without success.
Plug it in charger, and the light is intermittent orange (blinks once for about .75 seconds, every three seconds).

Where can I find replacement batteries?
The battery isn't blown up, and seems to be functioning, but I don't think I'll get a lot of charge out of it!
For future reference, I found a website going into the details on the EzReader or the LBook V3 variants (they seem to use the exact same type of battery, type V5-364560):

https://e-ink-reader.ru/batt_en.php