MAcbook Pro turning off with battery still charged

Hi all,

I have a 2014Macbook pro 15"

Recently I have had the following problem. If i turn off my macbook and it has less than 50% battery left, when I next turn it on, it loads up to let me log in, I can see there is between 0-50% battery I log in and then it turns off. If i leave it for a few minutes and press the power button again the screens shows the sign asking me to charge it up. If I then plug in the charger and turn it on it loads up straight into OSX without needing to log in and shows the correct batter charge, ie if there was 20% when I turned it on originally it would have 20% now and then charge fine.

This problem doesn't seem to occur if I have more than 50% battery charge.

Any idea what could be going on?

Thanks

Danny