but at 40% charge i won't be getting the full usage of a 100% charge....

I also have an iriver h140 which ive had for around 4 years and am noticing a significant fall in the usage time of one full charge before it dies i.e. when it was new, a full charge = around 12-14 hours, but now only 6-7 hours How long will the clix2's battery maintain its supposed 24 hours usage time before it starts getting worse, or more importantly, how many years before the battery life dies out completely?