Here is how to use NOCO Genius 2: connect the clamps in the right order, plug the charger in last, then press the mode button until the mode matches your battery. The steps differ a little for a battery still in a vehicle and one you have taken out, so follow the set that fits your setup.
Before you learn how to use NOCO Genius 2 on your battery, confirm its voltage and chemistry, because the mode you choose must match both. The charger is built for lead-acid, AGM and lithium batteries only.
What the NOCO Genius 2 Can Charge
The NOCO Genius 2 charges 6V and 12V lead-acid batteries, AGM batteries and lithium iron phosphate batteries, with a 2-amp output and a capacity of up to 40 Ah. According to NOCO’s specifications, it also maintains batteries of all sizes.
- 6V wet, gel, enhanced flooded, maintenance-free and calcium batteries
- 12V wet, gel, enhanced flooded, maintenance-free and calcium batteries
- 12V AGM batteries, using the 12V AGM mode
- 12V lithium batteries, only if they have a built-in battery management system (BMS)
Do not use the charger on other battery chemistries. NOCO warns that charging an unsuitable battery may cause injury, death or property damage, so contact the battery maker if you are unsure. If you need more than 40 Ah, NOCO Genius 10 charging modes covers a 10 amp model up to 230 Ah.
Before You Connect the Charger
Before you learn how to use NOCO Genius 2 in practice, confirm the battery’s voltage and chemistry, then set up the charger in a dry, ventilated spot away from fuel and sparks. NOCO’s guide says not to use the charger on other battery chemistries.
- Work in a well-ventilated area and never cover the charger.
- Do not smoke, and keep sparks and open flames away from the battery.
- Wear eye protection, because batteries can explode and throw debris.
- Remove rings, watches and metal tools before you touch the terminals.
- Keep the charger between -4°F and 104°F (-20°C to 40°C), and never charge a frozen battery.
- Plan the cable run. The DC cable is about 77 inches long, and NOCO advises 12 inches of slack between connections.
Stop using the charger if the battery becomes excessively warm, if a cord or casing is damaged, or if the unit gets wet. NOCO says a damaged product should not be used at all.
How to Use NOCO Genius 2: Connecting the Clamps
For how to use noco genius 2 safely, connect the red clamp to the positive terminal and the black clamp to a metal ground, then plug the charger into the wall last. Clamp order is the step people most often get wrong, so check the polarity of the battery before you connect anything.
According to NOCO’s GENIUS2 user guide, the positive terminal is marked POS, P or +, and it is usually the larger of the two posts. The negative terminal is marked NEG, N or -.
Battery still in the vehicle
Most vehicles are negative-grounded, meaning the negative terminal is connected to the chassis. Find out which terminal is grounded, then follow these steps.
- Position the AC and DC cords away from the hood, doors, fan blades, belts and pulleys.
- Connect the red clamp to the positive terminal that is not grounded.
- Connect the black clamp to a heavy metal part of the frame or engine block, away from the battery.
- Plug the charger into a suitable outlet, and do not face the battery when you make that connection.
Battery out of the vehicle
With the battery on a bench or on the ground, start by attaching a cable to the negative terminal. This moves the last connection away from the battery, where a spark is less likely to reach it.
- Attach at least a 24-inch, 6-gauge insulated cable to the negative terminal.
- Connect the red clamp to the positive terminal.
- Stand as far from the battery as practical, then connect the black clamp to the free end of the cable.
- Plug the charger into an outlet.
Never clamp to a carburetor, a fuel line or thin sheet metal. When you finish, unplug the charger first, then remove the negative clamp before the positive one.
Choosing a Charge Mode
The core of how to use noco genius 2 is the mode: press the mode button to cycle through them, and pick the one that matches your battery’s voltage and chemistry. The 6V mode is for 6-volt lead-acid batteries only, and the 12V Lithium mode is for lithium batteries with a BMS only.
| Mode | Peak voltage | Use for |
|---|---|---|
| Standby | No power | Idle state, orange LED, used on first use |
| 12V | 14.5V | 12V wet, gel, enhanced flooded, maintenance-free and calcium batteries |
| 6V | 7.25V | 6-volt lead-acid batteries, entered by pressing and holding for 3 seconds |
| 12V AGM | 14.8V | 12-volt AGM batteries |
| 12V Lithium | 14.6V | 12-volt lithium batteries with a built-in BMS only |
| Force | Batteries under 1V | Batteries too low for the charger to detect, entered by pressing and holding for 5 seconds |
Peak voltages are measured at 25°C, and the charge current is 2 amps in each active mode. Check the battery maker’s rules if the label is unclear.
Starting a Charge and Reading the Lights
When you first use NOCO Genius 2, the charger starts in Standby with an orange light, so you press the mode button to select your mode and begin charging. Once the mode is set, the charge lights show how full the battery is, which finishes how to use noco genius 2 for a normal charge.
- Confirm the battery voltage and chemistry, and confirm the clamps are connected correctly.
- Plug the AC cord into an electrical outlet.
- On first use, the charger starts in Standby. It provides no power in this mode.
- Press the mode button until your battery’s mode lights up. Press and hold for three seconds to enter an advanced mode.
- The mode light and the charge lights come on, which means charging has started.
The charger has auto-memory. When you reconnect it, it returns to the last mode you used, so you only need the mode button when you change modes. The 1 amp NOCO Genius 1 mode guide also has auto-memory, for smaller batteries.
| Light | What it means |
|---|---|
| Red 25% | Pulses while the battery is below 25 percent, then stays solid at 25 percent |
| Red 50% | Pulses while the battery is below 50 percent, then stays solid at 50 percent |
| Orange 75% | Pulses while the battery is below 75 percent, then stays solid at 75 percent |
| Green 100% | Pulsing means bulk charge is complete and the battery is being optimized; solid means fully charged |
After the battery is full, the charger keeps monitoring it and provides maintenance charging. The 100% light pulses slowly during these cycles, and NOCO says the charger can stay connected indefinitely.
How Long a Charge Takes
For how to use noco genius 2 on a large battery, plan the wait: a 40 Ah battery takes about 15 hours, while an 8 Ah battery takes about 3 hours, according to the reference chart in NOCO’s user guide. Those figures are estimates, not guarantees.
| Battery size (Ah) | Approximate charge time (hours) |
|---|---|
| 8 | 3.0 |
| 12 | 4.5 |
| 18 | 6.75 |
| 24 | 9.0 |
| 40 | 15.0 |
The chart assumes about 50 percent depth of discharge, so a deeply drained battery takes longer, and temperature also affects the time.
A battery that will not hold a charge may never reach the times in the chart, so check it if the charge seems to stall.
Force Mode and Error Lights
The last part of how to use noco genius 2 is handling faults: Force mode lets the charger start on a battery with less than 1 volt, and a solid red light signals a fault that needs checking before you continue. Force mode disables some safety features, so use it only when the battery is too low for the charger to detect.
To enter Force mode, press and hold the mode button for 5 seconds, then select the charge mode. Force mode runs for five minutes before the charger returns to normal charging. Connect every clamp first, because live power is present at the connectors and the clamps must never touch each other. If the battery is too weak to charge, a jump starter is a different tool, explained in the NOCO GB20 jump start guide.
| Light | Meaning | What to do |
|---|---|---|
| Solid red, overvoltage | Battery voltage is too high for the selected mode | Check the battery and the charge mode |
| Solid red, bad battery | The battery will not hold a charge | Have the battery checked by a professional |
| Solid red, reverse polarity | The clamps are connected to the wrong terminals | Reverse the battery connections |
| Flashing | Charger is too hot or too cold to run | Wait, since it resumes when the temperature returns to range |
Frequently Asked Questions
Can the NOCO Genius 2 charge a lithium battery?
Yes, but only in the 12V Lithium mode, and only for 12-volt lithium batteries that have a built-in battery management system. NOCO says some lithium batteries are unstable and unsuitable for charging, so contact the battery maker for the recommended rates before you start.
Why won’t the NOCO Genius 2 start charging?
Start by checking the clamps, the first step in how to use noco genius 2 correctly. A solid red reverse polarity light means the clamps are on the wrong terminals. If the battery voltage is too low for the charger to detect, use Force mode after confirming every connection, and remember that it runs for five minutes only.
Can I leave the charger connected all the time?
Yes. After the battery reaches full charge, the charger keeps monitoring it and provides maintenance charging. NOCO’s guide says it can stay connected indefinitely, though you should still stop if the battery becomes excessively warm.
What does a flashing light on the charger mean?
A flashing error light means the charger is too hot or too cold to work. It resumes once the temperature returns to the operating range of -4°F to 104°F. Move the charger to a suitable spot and let it settle before you check the connections again.
If a solid red light appears after you have checked the clamps and the mode, stop charging and have the battery inspected by a professional. Damaged or incompatible batteries can explode or catch fire, so an error light is a signal to get help, not to keep trying.
