MacBook 12” (Early 2016) Start up / Battery issues

I have two issues, I believe they both may be interlinked but cannot find any answers as to what is causing them!

1) If the MacBook is charged above 70% then if I attempt to restart the laptop, regardless of what the battery is on at that point I am faced with a flashing folder with a question mark. This then leads to requiring either internet recovery or CTRL + Option + P + R.

2) The same flashing folder appears if the laptop ‘dies’. This is more recent, as soon as charge hits about 16-17% the laptop will, without warning, shut down and it appears to be because of flat battery. However, upon restarting (after using the above mentioned steps) the charge bumps from 0% to 18% almost immediately.

Does anybody know what could be causing this? I’m essence I am stuck only being able to use my MacBook when it is between 18% - 68% charge!!!