Yes, they will still charge but at a significantly reduced rate and energy. Solar panels utilize daylight photons and not just direct heat or bright sunshine to charge the battery. For overcast sky or partial shade, charging efficiency can drop by up to 50%-70%. Expect much shorter runtimes on cloudy days.

Standard solar landscape lights require about 6 to 8 hours of unshaded direct sunlight to achieve a full charge. A fully charged battery typically provides 8 to 10 hours of illumination, easily lasting from dusk until dawn.

Before assuming that the product is defective, check the most common oversights: [1] Many models have a hidden, waterproof master ON/OFF switch, it must be switched ON for the product to work at night or in the dark. [2] It is highly recommended to let new solar lights sit in direct sunlight for at least 24 hours to 47 hours with the switch turned OFF before using them the first night. This primes the rechargeable battery for a full lifecycle.

The built-in rechargeable batteries (usually NiMH or Lithium-ion AA/AAA sizes) typically lasts 1 to 3 years before losing their capacity to hold a charge. If your lights only stay bright for an hour or two after a perfectly sunny day, it is a clear indicator that the battery needs to be replaced.

This is almost always caused by ambient light interface. Solar lights feature a built-in photocell (dusk-to-dawn sensor). If you position your solar lights too close to a bright source (i.e. nearby streetlamp, floodlights, etc.), the sensor gets tricked into thinking it is still daytime and shuts the LED off. Moving the fixture a few feet into a darker pocket resolves this.

Wiping the panels down with a damp microfiber cloth every few months is highly recommended. Dust, pollen, bird droppings, and hard-water spots from garden sprinklers or rain can build a cloudy film over the solar panel, blocking potential solar energy from reaching the photovoltaic cells beneath.