Turn off the control knobs for the grill burners, and wait for the appliance to cool completely if it has been burning.
Shut the gas valve in the line connected to the grill, turning the handle on the valve clockwise.
Remove the cover on the battery compartment behind the grill's control panel or mounted just below the control panel. The cover may slide off, or it may be secured with a single screw that must be removed before you can take off the cover. On select models, the battery compartment unscrews to reveal the battery underneath.
Remove the old battery. If it is a 9-volt battery, then disconnect the two posts on the top of the battery from the contacts wired to the battery compartment. Snap off the contacts' vinyl cover to detach the battery. Do not pull the wires on the vinyl cover.
If you remove a AA-size battery, note the terminal polarity on the battery as it relates to the contacts on the compartment. The bump on one end of the battery is the positive (+) terminal.
Insert a replacement battery. If it is a 9-volt battery, snap the contacts' vinyl cover onto the battery, and insert the battery into the compartment. If the replacement battery is AA size, match the battery's terminal polarity to the contacts on the compartment. The positive (+) terminal is the bump on one end of the battery.
Replace the cover on the battery compartment. Depending on your grill model, slide the cover into position, secure it with a screw or twist the cover's cap clockwise to screw it in place.
Open the gas valve.