Your device probably has a battery gauge that's drifting upwards and hasn't been really fully charged for several days. It hence miscalculated the remaining percentage and dropped to zero when it was actually empty. If, on the other hand, it was recently fully charged (not just showing 100% but having power for another hour or so after that), then this might indicate a cell balancing issue. Both are well known issues with the SBV and I hope Zendure will address those with a firmware update.