What the NOCO GENIUS lights mean
Pulsing red on a GENIUS1 means the battery is under 75 percent and charging. Pulsing green means the main charge is done, solid green means full, and a slow green pulse means it is maintaining the battery.
Checked against sources on by the TrueAmps editorial team.
Charge level lights
| Light | GENIUS1 | GENIUS2 |
|---|---|---|
| Pulsing red | Under 75% charged | Under 25% or under 50% (two red LEDs) |
| Pulsing orange | not used | Under 75% charged |
| Pulsing green | Over 75%, main charge done | Main charge done, optimizing |
| Solid green | 100% charged | not listed |
| Slow pulsing green | Maintenance, can stay connected | Maintenance until disconnected |
From NOCO's GENIUS1 and GENIUS2 support pages, checked September 24, 2026.
Error lights
| Error | What NOCO says | What to do |
|---|---|---|
| Standby | Charger in standby, or battery voltage too low to detect | Select a charge mode; below 1 V, NOCO provides Force Mode |
| High Voltage | Battery voltage too high for the selected mode | Check the battery and the mode |
| Bad Battery | Possible short, or battery will not hold a charge | Have the battery checked by a professional |
| Reverse Polarity | Clamps connected the wrong way round | Swap the connections |
| All error lights flashing | Too hot or too cold | Wait; it resumes within its temperature limits |
Modes, and the one to be careful with
The GENIUS1 and GENIUS2 have a 12 V mode for wet, gel, enhanced flooded, maintenance-free and calcium batteries, a separate 12 V AGM mode, a 12 V lithium mode that NOCO limits to batteries with a battery management system, and a 6 V mode. What the AGM mode changes.
Force Mode is for batteries below 1 volt. In the GENIUS5 manual NOCO writes it in capitals: use it with extreme care, because Force Mode disables safety features and the connectors are live (GENIUS5 user guide). Make every connection before you start it.
How long a full charge takes depends on the battery and the charger. The charge-time calculator uses NOCO's own tables.
Questions people ask
Why is my NOCO GENIUS1 flashing red?
A pulsing red charge LED on the GENIUS1 means the battery is less than 75 percent charged, according to NOCO. It is charging normally.
What does solid green mean on a NOCO GENIUS1?
The battery is 100 percent charged. Afterwards the LED pulses green slowly while the charger maintains the battery, and NOCO says it can stay connected.
Why are all the error lights flashing on my NOCO GENIUS?
NOCO lists that as a temperature fault: the charger is too hot or too cold. It resumes on its own once the temperature is back within its operating limits.
What is the Bad Battery light on a NOCO GENIUS?
NOCO describes it as a possible battery short, or a battery that will not hold a charge, and advises having the battery checked by a professional.