The most common issue is the battery. It could take up to five days for a new solar unit to cycle to full capacity. Winter months will affect this cycle time as well, if installed in the middle of winter. To test a solar unit remove the Ni-MH batteries, and install size AA alkaline batteries. Cover the entire solar collector to test the unit. If the unit lights up, replace the Ni-MH batteries. Do not leave alkaline batteries in the unit.