Do these lights need wiring or an electrician?

No. Each light has its own solar panel and battery, so you only screw the bracket to the wall. Place them where the panels get direct sun for most of the day.

How long do they stay on at night?

Runtime depends on how much sun the panels got that day. After a full sunny charge they typically run for several hours; after cloudy days, expect a shorter night and dimmer light.

Can I replace the batteries or LEDs?

On most units of this type the LED and battery are sealed inside the housing. Treat them as long-life consumables rather than serviceable parts.

Where should I mount them for the best effect?

Mount them on a flat exterior wall, fence or pillar at roughly eye-to-chest height so the up-and-down beams wash the surface. Keep panels clear of shade from trees or eaves.

Are they bright enough to light a path or steps?

They work as accent and ambient light, not as security lighting. For steps and walkways, space them closely and treat them as guidance lighting rather than full illumination.