Control panel shows E05 and the generator will not crank; no starter noise is heard.

Safety first: Turn the generator OFF and isolate the ATS. Wear eye protection when working around batteries.

• Measure battery voltage: Using a digital multimeter, measure across the battery posts. A healthy 12 V battery should read around 12.6 V at rest. Below ~11.8 V indicates deep discharge.
• Inspect terminals and cables: Check for white/green corrosion on battery posts and cable lugs. Clean with a baking soda solution, rinse, dry, and tighten connections securely.
• Check AC supply to charger: Confirm that the Genergy battery charger is receiving utility power (if it is an AC‑fed charger). Verify the charger input breaker or fuse is not tripped.
• Test charger output: With AC present, measure DC voltage at the charger output leads. It should be around 13.4–13.8 V for a 12 V system. If zero or very low, the charger is likely faulty.
• Charge or replace battery: If the battery is older than 3–5 years or fails a load test, replace it with a battery type and CCA rating recommended by Genergy. Clear the E05 code and attempt a start.

If the new battery discharges again quickly, the onboard charger or wiring is suspect and should be tested by a qualified technician.