Might still have the battery from my S3 if you want to see if it's got more life left in it;
I gave my S1 to O'Shane when I got my S3, think it lasted at least 3 years from new, better because with CyanogenMod installed it didn't suffer too much from losing space to bundled/upgraded app versions.
My S3 is now our work phone, my S5 is still going well apart from a small screen crack. S5 is loads better than the 3 and must be cheap by now.