Controller displays LOW BATTERY or BATTERY LOW; generator may crank slowly or fail to crank.

Safety first: Place the controller in OFF and open the main breaker. Wear eye protection when working around batteries.

• Inspect battery terminals: Check for white or green corrosion on posts and cable ends. Clean with a baking soda solution and a wire brush, then tighten securely.
• Measure battery voltage: Use a multimeter; a healthy fully charged 12 V battery should read about 12.6–12.8 V with the unit off. If below 12.0 V, charge or replace the battery.
• Check Guardian battery charger: With AC power present, measure voltage at the battery; it should be around 13.2–13.6 V. If not, the onboard battery charger module may have failed.
• Replace battery if needed: Install a new battery of the type and cold-cranking amps specified by Guardian. Ensure correct polarity and secure mounting.
• Reset alarm: After correcting, clear the alarm and perform a manual exercise run to confirm reliable cranking.