The solar lamps have built-in solar panel and battery. The solar panel has a photosensor through it at dusk automatically switches on and at the morning off. You will not have to worry about turning it on and off! During the day the solar panel collect energy in the rechargable battery.
During the night the energy is being consumed. Each battery has a certain life, which depends on the number of charges and discharges. (Average life of a battery lasts about a year and a half.) You will not have to replace the batteries over a year!
Batteries can be replaced. You only need to obtain exactly the same battery.