You have to remember that an 80% charge is just barely 10 bars of charge. Getting 9 bars on a 80% charge is pretty normal, though most people have typically seen that when it's hot out and not in cool Santa Cruz.
Now - how often do you charge to 100%? If you haven't done that in a while, charging to 100% may help you get to 10 bars when L2 charging more consistently.
I wouldn't worry your CS-40 - it is working properly.
If you're curious about 9-bar 80% charge thing, this is the big thread with all the details - I suggest continuing further discussion there.
80% Charge only 9 bars?