I think it depends on a lot of factors such as how hot it gets (do you ride in Phoenix with 110F weather)? Is it stored in a garage with sub zero temperatures? I have first gen Ultegra Di2 on my 2012 BMC and am still using the original battery. I never ride below freezing, it's stored at room temperature and rarely ride when it's over 90F. I put about 5k miles a year on it and charge it 4-5 times annually. So it probably only has 28-35 charge cycles. If batteries last 300 charge cycles I think it still has a bit of life left.