Upgrade to 8.1 Pro or keep 7 Ultimate??

So I have a Windows 7 Ultimate laptop that is VERY OLD (almost 2 decades old) and my parents have the Windows 8.1 Pro Disc for the full version that has been with them since 2014, and keep in mind I am in Syria and this was brought from Europe, specifically Ireland. The battery life has gotten very bad, unplugged = 5 minutes then dies, additional battery is broken, but everything else just seems fine! I don't know what to do though, should I upgrade to Windows 8.1 or stay? The box is very great btw, and the battery life has gotten worse probably when we made it go from 32-bit to 64-bit. Un-sure.