The battery life isn't dependent on the OS alone, it really depends on what you are doing with the machine. If you were to do basic thing like browsing the web, writing documents, no video streaming or something, you'll get a good many hours of use on the battery. Try running some serious applications (photo/video editing, CAD, scientific) and you will not get anything remotely to what is advertised..
So the real question is based on your current usage and current OS (neither of which you have stated) will High Sierra do a better job with the battery life. My guess is that High Sierra will work as well as Sierra but since it's a "tweak" version of Sierra, likely won't have a lot of features/functionality..