Let's just be real here.
If you had this Apple Pencil for a month or even longer period of time and it has not been charged up for all that time, your Apple Pencil is dead and you will need to purchase a new one.
Sorry.
FYI and something Apple never divulges to it potential iPad Pro/Apple Pencil customers/users unless the potential customer/user is smart enough to ask about.
Due to the “always on an active/stanby” nature of the Apple Pencil and, also, due to its very tiny rechargeable Li-ion battery (smaller than the eraser head on a REAL pencil), the Apple Pencil needs to be constantly charged up to some significant charge level ALL THE TIME, even when not using the Pencil for prolonged periods of time.
The Apple Pencil needs to be kept charged to a minimum of 5-10% all the time.
If the Apple Pencil battery is allowed to drain down to 0% and allowed to stay in that flat condition for more than a few weeks, or so, OR EVEN LONGER, that very tiny little Li-ion battery is too small to keep at a 0% state for a long period of time and it will fail and the Apple Pencil will be dead and you may have to “pop” for another $99 Apple Pencil, once again!
This is definitely a big flaw with the Apple Pencil.