I got the same problem. I have try reset SMC & PRAM, remove battery & RAM, reinstall MacOS High Sierra z which all does not work.
My battery condition show Normal & actually i just change the new battery two months ago only so it's new & does not charge many cycle.
I suspect might be because install some software & crush the system in MacOS high Sierra.
As after i upgrade the MacOS High Sierra, it's working normal but after I upgrade the software due to compatible problem. It start to have this problem. I had tried to uninstall some program but still some did not do it yet as I need to finish some project on it & I afraid can't get back the software later so did not try yet. After I finish the project, will back up the data & try to uninstall all the upgrade software.
Might be you can try if you got the similar situation or if you have already solved your problem, kindly keep me update.
I will update the result after I uninstall all the software too.
Let's keep in touch !