Hi everyone. I just purchased a brand new Macbook Air 13 inch literally just yesterday, and I was loving it. However after I started to charge it when it went down to 38 percent, I kept on charging it till 100 percent, but when I checked my battery life it had gone down to only 9 hours from the original 13 hours I had. When I first turned my macbook on yesterday it had a capacity of almost 13 hours. The apple website also promises up to 12 hours on this particular macbook as well. Is this only temporary? Or do I have a sub par battery?. Im also not running any apps or any programs and that battery life has stayed at 9 hours capacity still. Sorry about the bad english, not really too fluent..