The duration a fully charged solar flashlight lasts depends on several factors, including the battery capacity, the efficiency of the solar panel, and the output settings of the flashlight. Generally, most solar flashlights can last anywhere from a few hours to over a day on a full charge. Models with lower power settings or efficient LEDs may provide light for longer durations, sometimes up to 12-24 hours. However, usage patterns, such as using higher brightness settings, can reduce this time.