The battery runtime of headlamp will determine the number of hours the light can be operated at full power. Also, it indicates how efficient the headlamp uses its battery power. In general, the runtime can be at least 3 – 4 hours and if it is even more, then it might have a heavy battery. How bright the light produced/used by the lamp will determine how long it’s battery last. So, choose a headlamp with decent runtime and average beam length to complete your task.