MacBook Air won’t wake up if not connected

Hi all. I have the following problem for some time now on my MacBook Air 13″ mid 2014: if I close the computer with less than 50% of battery it won’t wake up, I need to connect it to an outlet. But this morning it was fully charged when I left home and when I tried to use it it wouldn’t start, it showed me the low battery icon and that was it. I returned home and connected and then it started, but it was 98% cherged! Any ideas?
Thanks in advance