For electric stunt, everyone I know, and myself included, starts with a fresh charge. After some experience, one gets to know how long a charge will last. Since LiPO cells must never be run completely down, we always put the battery back on charge long before they get low enough to cause any flight problems.
I guess it's true that the R/C guys routinely run flight batteries until they quit. That is OK for R/C, but not C/L.
Floyd