There is "NoNotifications", which can intercept notifications and even hide specific ones based on the text they contain
However, when I tried to install it, it failed. Let me know if you get it working.
I also saw a suggestion to uninstall the power indicator
sudo apt remove indicator-power
But this gave me an error that it wasn't installed in the first place. Perhaps it goes by another name now, in Ubuntu 18.04?
I post this answer to point out how many times I've seen this asked in all my searches, and while there are fixes that may have worked in Ubuntu 17.10 and below, they no longer work in 18.04. And too many replies take a condescending "change the batteries" (when in fact these low powered devices will continue to operate on batteries for months or even a year while this notification still pops up) or "this has already been answered" (pointing to these fixes which no longer work), and so, I think we have a bug on our hands.
However, I too do not know what "package" to report (as you also mentioned in one of your comments). Typing "ubuntu-bug" in a terminal and answering "Other" says "You need a PID"...