Assuming batteries are fully charged and relatively new (within 12 months of purchase), the unit will stay lit continuously for about 85 minutes. Be advised that brightness will begin to diminish (i.e., dim) as the batteries discharge. Once batteries are fully discharged, allow more time for batteries to charge to sufficient levels. (Otherwise, unit may not activate as expected the following night). To fully recharge batteries, turn the unit OFF (via control switch underneath mounting canopy, see instruction manual for more details) for a period of 2-5 days. This will allow batteries to charge via solar power without discharging at night.