The battery indicator isn’t very precise due to small number of «bars». It might show full at, say, 80-100% range. So it could be early 80% when you think it’s fully charged, getting to 79% when you start it the second time, showing you an empty bar.
Better check more precise battery status via Settings > System Settings > Info > (scroll to the Power line).
Charge your Clip, check the digits and leave it for few hours. If you see an alarming difference on restart — there’s most likely a hardware problem and you need to exchange it. But keep in mind that small fluctuations can occur here as well, as the power status code on such devices is usually rather approximate.
