Ah, ok. I am sorry- I failed to fully understand.
I am not really sure if this will work, so please post along with your progress... But check if you have this file:
/etc/UPower/UPower.conf
On mine, starting around line 65 there is the following:
PercentageLow=10
PercentageCritical=3
PercentageAction=2
Change the above values to double:
20, 6 and 4 respectively. Then save and exit the file.
In terminal please enter:
sudo systemctl restart upower
Reboot or log out and in and check if you are getting notifications.
(May need to wait until battery gets low...)