I'd consider 4.5 years quite good to be honest. I still dislike the idea of built-in expiration date, but it's still a good time. Average is probably lower and closer to 2 years. LiIon batteries usually survive around 600-1000 charge cycles, more if you don't use top 20% of the voltage range but no one is doing that these days. Maximum capacity starts dropping really fast, after some 2-3 months of use, as it's frequently noticed with laptop batteries. So I'd say 4.5 years is about at the tail end of that expected maximum life. Wish they made batteries replaceable. But soon they will be thanks to EU.