Can I upgrade my iPhone 4s to 8.1.2?

I am using iOs 7.1.1 on my 4S. But I am not happy with battery backup. It is worst when compared to my 3GS running on 6.1.2. Review say 8.1.2 is still more worse than ios 7 when comes to battery issue. I dont use much for browsing, watching videos...I just use my phone as to make or take calls. If I upgrade to 8.1.2. then my problem is solved?