You can use the power of the sun to illuminate your garden at night, and at the same time save fossil fuels, by using solar lights. Each light has a small solar panel that charges one to four rechargeable AA nickel-cadmium batteries, which power the light when the sun goes down. These batteries last one to two years and need to be replaced when the light is dim at night or doesn't stay on for very long. While lamp styles vary, most allow for easy battery replacement.
Charge the new batteries in a wall charger plugged into an electrical socket if they are not already charged.
Remove the cover from the solar light. You may have to unsnap it, unscrew it or twist it off, depending on the lamp. The solar panel is usually built into the cover, and you should find the battery case directly under the panel.
Open the cover of the battery case by unscrewing it or unhooking the tab holding it closed.
Remove the old batteries by pulling them out. You may be able to do this by hand, but if not, hook the screwdriver under each battery in turn and pry it loose.
Set the new batteries into the holder. Look at the battery cover to find out which way they should be installed. The positive terminal of each battery should be installed on the end that is marked with a '+' sign. If there are no markings, install each battery with the positive terminal, which is the terminal with the nub on it, on the end opposite the spring in the battery holder.
Replace the battery cover by snapping or screwing it back on. Then replace the lamp's cover by reversing the procedure you used to take it off.
Clean the panel on your solar light periodically to remove dirt and grime that may prevent the panel from fully charging. If you need to test the light while the sun is out, cover the panel with your hand to disengage the charger and activate the bulb.
Do not use regular alkaline batteries in a solar light. They will not recharge and may leak when subjected to the charging current from the panel.