Battery Charger Reports Abnormal Battery During Float

Common Symptoms

• Generator displays code 1518 on the Evolution controller panel
• Yellow alarm light is solid or flashing on the control panel
• Generator may still start and run but logs a charger warning in fault history
• Weekly exercise cycle completes but code 1518 remains stored
• Battery voltage reads low or erratic on the panel display
• OnCue or Mobile Link app shows a charger warning notification
• Generator passes self-test but returns 1518 fault on next check

Probable Causes (Ranked by Likelihood)

• Worn or sulfated battery that can no longer accept or hold a float charge Very Likely
• Battery age exceeding 3-5 years causing degraded internal cell capacity Very Likely
• Loose, corroded, or high-resistance battery cable connections preventing proper charge transfer Likely
• Faulty or failed onboard battery charger (trickle charger) circuit on the controller board Possible
• Battery terminals with corrosion building resistance between charger and battery posts Possible
• Extreme cold reducing battery capacity below the charger's acceptable float threshold Less Likely
• Wiring harness damage or open circuit between controller charger output and battery Less Likely

Step-by-Step Diagnostic Procedure

1. Start with a visual inspection. Open the generator housing and locate the 12V standby battery. Look for corrosion (white or bluish buildup) on the terminals, cracks in the battery case, or swelling on the sides of the battery. Any of those signs points to a failed battery.

2. Check battery voltage with a multimeter. Set it to DC volts. Touch the red probe to the positive terminal and the black probe to the negative terminal. A healthy battery at rest should read 12.4V to 12.7V. A reading below 12.0V at rest means the battery is weak. A reading below 10.5V means it is likely dead.

3. Inspect the battery cable connections. With the generator in the OFF position, wiggle each cable at the battery post. They should be tight with no movement. Use a wrench to snug any loose terminals. If you see green or white powder, clean the terminals with a wire brush or a baking soda and water solution, then dry thoroughly.

4. After cleaning connections, turn the panel to AUTO and let the onboard charger run for 4 to 8 hours. Then recheck battery voltage. If voltage climbs back to 12.6V or higher and the code clears, the problem was likely a connection issue.

5. Load-test the battery if you have access to a battery load tester, or take the battery to an auto parts store for a free load test. A battery can show 12.6V at rest but collapse under load. If the battery fails a load test, replace it. Generac recommends a Group 26R or equivalent 12V standby battery depending on your model.

6. If the battery and connections test good, check the charger output from the controller. With a multimeter on DC volts, measure across the battery terminals while the generator is in AUTO mode with no fault active. You should see a float voltage of approximately 13.2V to 13.8V from the onboard charger. A reading at exactly 12V with no rise indicates the charger circuit may not be working.

7. If charger output is absent and the battery and cables are confirmed good, the onboard charger circuit on the controller board is likely the cause. This repair requires replacing the controller board or sending it for service. Call a certified Generac dealer at this point.

8. Clear the fault by pressing the OFF button, then pressing AUTO to reset. If code 1518 returns within a few days without a clear cause, document the battery age and voltage readings before calling a technician.

Frequently Asked Questions