Your battery is just reaching the end of its lifespan. Mine completely died at 1500 cycles at 0.0% charge.
I used to be able to get it to 100% by plugging the charger in and out repeatedly, but it drained in minutes.
The best thing you can do is increase the battery warning and critical warning at 45% or more and just never let it go down past 40%.
You could buy a replacement battery, but that gets complicated given how difficult it is to remove the battery. A computer repair store could if you can't.
I've tried a lot of things, calibrating it, draining it to give a full cycle, holding the power, etc. Nothing works. It just needs to be replaced.