the optimal charge state for long-term storage of a lipo cell is about 33%. 50% is a nice buffer on top of that if you use it unplugged for an hour or so, then put it away.
maybe not, but it's probably not much worse than the optimal charge state. you want to keep a lipo cell at 3.7v for optimal longevity. usually this corresponds to above 20% charge but below 80%, but the concept of "charge level" is sort of arbitrary. the manufacturer has already set safety buffers on either end of the spectrum, but the exact amount will vary based on risk tolerance, application, etc.
