Charger Missing AC Generac (Code 2780): Meaning & Safe Checks

Updated: February 1, 2026

If your Generac shows “Charger Missing AC” (Code 2780), it means the generator’s built-in battery charger isn’t receiving the 120V AC input it expects. This is usually related to the T1 circuit from the transfer switch. Here’s everything you need to know about this warning and what to do next.

What Does “Charger Missing AC” Mean?

On Generac standby generators, “Charger Missing AC” appears as Warning Code 2780. The generator’s built-in battery charger requires 120V AC power (typically through the T1 circuit from the transfer switch) to keep the starter battery charged.

When this AC feed is missing or abnormal, the controller displays this warning. Without a charged battery, your generator won’t start when you need it most.

Generac Error Codes Related to Charger/Battery Issues

Tip: Take a photo of any code displayed. This helps technicians diagnose faster.

Common Causes of Charger Missing AC (Code 2780)

Troubleshooting: What to Check (Safe Steps Only)

These are safe observations you can make without opening panels or touching wiring:

Step 1: Note the Timing

• Did this start during or right after a power outage?
• If yes, this is often temporary. Monitor for 24-48 hours after utility power stabilizes.

Step 2: Check the Controller Display

• Take a photo of the exact message/code
• Note any other warnings (red light, additional codes)
• Check if the display shows time/date correctly

Step 3: Document Battery Age

• If you know when the battery was installed, note this
• Batteries typically last 3-4 years in standby generators
• If also seeing “Inspect Battery” warnings, replacement may be needed

Step 4: Monitor After Power Stabilizes

• If the warning clears and stays clear, it was likely outage-related
• If it returns within a week, schedule service

When to Call a Professional

Contact a qualified Generac technician if:

1. Warning persists 48+ hours after utility power is stable
2. Warning keeps returning after it initially clears
3. You see multiple warnings (red alarm light + Charger Missing AC)
4. Weekly exercise fails along with this warning
5. Generator won’t start when needed

Understanding the T1 Circuit

The T1 circuit is how your Generac’s battery charger gets power. Here’s a simplified explanation:

• T1 and T2 are load terminals on the transfer switch
• They connect to N1 and N2 terminals respectively
• The T1 circuit provides 120V AC to the internal battery charger
• If this circuit is interrupted (blown fuse, loose connection, transfer switch issue), you’ll see Code 2780

This is why the warning often appears during outages. The transfer switch is actively working, and if there’s any interruption in the T1 feed, the charger loses its AC input temporarily.

Replacement Parts (Only If Confirmed by Service)

If a qualified technician confirms your charger needs replacement, have the correct part ready. Always verify compatibility with your exact model and serial number before purchasing.

• 705927 Battery Charger Replacement for Generac – Compatible with many Guardian models
• FITE ON 12V Power Adapter for Generac 0G5744 – For specific model ranges

Important: Do not attempt to install these yourself unless you’re a qualified technician. Charger/transfer-switch wiring should only be handled by professionals.

Prevention Tips

• Regular maintenance: Annual service catches issues before they cause warnings
• Battery replacement: Replace proactively every 3-4 years
• Surge protection: Have an electrician install whole-house surge protection to reduce nuisance trips after outages
• Keep a log: Note when warnings appear, especially if related to outages
• Weekly exercise: Ensure your weekly test runs properly

Related Generac Warning Lights

For complete information on indicator lights, see our guide: Generac Generator Red Light On: What It Means

Conclusion

The “Charger Missing AC” (Code 2780) warning on your Generac is usually related to the AC power feed for the internal battery charger. While it often appears temporarily during power outages, persistent warnings indicate an issue with the T1 circuit, transfer switch, or charger system that requires professional attention.

Key takeaways:

1. Don’t panic if it appears during an outage, wait 24-48 hours
2. Never attempt electrical repairs yourself
3. Document the warning with photos and timing
4. Call a technician if it persists or returns

Will Charger Missing AC clear itself?

Sometimes yes, especially if it appeared during a power outage. Once utility power stabilizes (24-48 hours), the warning may clear automatically. If it doesn’t clear or keeps returning, you need professional service.

Can I reset the Charger Missing AC warning?

You can acknowledge it on the controller, but avoid repeatedly resetting as a “fix.” The warning exists for a reason. Document it and let a technician identify the root cause if it persists.

Is Charger Missing AC dangerous?

The warning itself isn’t dangerous, but it means your battery isn’t being charged. If left unaddressed, your generator may not start during an actual emergency when you need it most.

How much does it cost to fix Charger Missing AC?

Costs vary depending on the cause. A simple fuse replacement might be under around $100 with a service call. If the charger component needs replacement, parts run around $50-150 plus labor. Transfer switch issues can be more expensive.

What is the T1 circuit on a Generac?

The T1 circuit is a 120V AC feed from the transfer switch that powers the generator’s internal battery charger. If this circuit is interrupted (blown fuse, connection issue), you’ll see the Charger Missing AC warning.