Jump-starting a car with the NOCO Boost Plus GB40 takes four steps once the pack is charged: connect the clamps to the pack, attach red to positive and black to negative, press the power button, and start the engine. That is the sequence in NOCO’s GB40 user guide. The 1,000-amp lithium pack is rated for gasoline engines up to 6.0 liters and diesels up to 3.0 liters, with up to 20 starts per charge, according to NOCO.
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I bought my GB40 myself and keep it in my vehicle. This walkthrough follows NOCO’s user guide step by step, explains what each light means, and covers the Manual Override mode for deeply drained batteries, which needs extra care.
GB40 at a glance
| Spec | NOCO Boost Plus GB40 |
|---|---|
| Peak current | 1,000A |
| System | 12V |
| Engine rating | Up to 6.0L gas, 3.0L diesel |
| Starts per charge | Up to 20 |
| Battery | 24Wh lithium |
| Charging input | Micro-USB, 5V/2.1A |
| USB output | 5V/2.1A |
| Light | 100-lumen LED, 7 modes incl. SOS and strobe |
| Protection | Spark-proof, reverse polarity; IP65 |
| Weight | About 2.4 lb |
Sources: NOCO GB40 data sheet and user guide.
Before you start
- Check the charge. Press the power button and look at the charge LEDs. NOCO recommends a full charge before use.
- Confirm the battery is 12V. The GB40 is for 12V lead-acid and lithium vehicle batteries only.
- Turn off everything in the vehicle: headlights, HVAC, radio and phone chargers. This puts all of the pack’s current into the starter.
- Put the vehicle in park or neutral with the parking brake on.
- Inspect the battery. Do not jump a battery that is cracked, leaking or frozen.
How to jump-start a car with the GB40, step by step
- Plug the clamp cable into the GB40’s 12V OUT port. Make sure it is fully seated.
- Attach the red clamp to the battery’s positive (+) terminal.
- Attach the black clamp to the negative (−) terminal or a solid, unpainted metal ground point on the engine block or chassis, per the vehicle manual.
- Press the power button. The GB40 checks the connection. With correct polarity on a battery it can detect, the Boost indicator lights up and the pack is ready.
- Start the vehicle. Turn the key or press start as you normally would.
- Once the engine runs, press the power button to turn the GB40 off, then remove the black clamp first and the red clamp second.
- Let the engine run so the alternator can begin recharging the vehicle battery, and recharge the GB40 when you get home.
If the engine does not start, NOCO’s guide advises waiting before trying again rather than cranking continuously. Follow the rest interval printed in your user guide; repeated long cranks can overheat both the starter and the pack.
Jump-starting other vehicles
The same steps apply to motorcycles, ATVs, lawn tractors and boats with 12V batteries, as long as the engine falls within NOCO’s 6.0L gas and 3.0L diesel rating. On small powersports batteries, the terminals can be tight to reach; make sure each clamp bites onto clean metal rather than a plastic cover or painted bolt. On a boat, ventilate the engine compartment before starting, and keep the pack out of standing water even though it carries an IP65 rating. If a vehicle has a remote jump post under the hood, such as many cars with trunk-mounted batteries, use those posts as the owner’s manual directs.
Reading the lights
The GB40 uses LEDs to show charge level and status. In general, a lit Boost LED means it is ready to start; a warning indication means it has detected a problem such as reversed clamps or no battery voltage. Because NOCO revises its LED codes between product revisions, check the table in the user guide that came with your unit for the exact meaning of each pattern.
Manual Override: for batteries too flat to detect
The GB40’s safety system will not send current unless it detects a battery. If a battery has dropped below about 2V, NOCO’s guide says the pack may not see it. For that case there is a Manual Override: hold the Manual Override button for three seconds to force power to the clamps.
Use it carefully. NOCO notes that Manual Override disables the spark-proof and reverse-polarity protection. Before using it:
- Double-check red is on positive and black is on negative.
- Never let the clamps touch each other.
- Only use it on a 12V battery.
A battery that has sat completely flat for a long time may be damaged. If the car starts but the battery will not hold a charge afterward, have it tested.
Worked example: how many starts are left? (estimate)
NOCO rates the GB40 at up to 20 starts per charge. If each start takes about 3 seconds of cranking on a small engine, that is plenty for a road trip. A larger V8 in cold weather draws more current for longer, so expect fewer starts per charge. Recharging after any use is the simplest way to stay covered; see my GB40 charging guide for how long that takes.
Using the GB40 as a power bank and light
- USB output: 5V/2.1A, enough to top up a phone in an emergency.
- Flashlight: 100 lumens with seven modes, including SOS and strobe, which I found handy under the hood at night.
Every phone charge uses some of the 24Wh battery, so recharge the pack afterward if you might need to jump a car.
Quick-reference checklist
Save this for the moment you need it. It condenses the steps above into one table:
| Step | What to do | Common mistake to avoid |
|---|---|---|
| 1. Prep | Car in park, ignition off, accessories off | Leaving the headlights or blower fan on |
| 2. Cable | Seat the clamp cable fully in the 12V OUT port | A half-inserted plug that only connects some of the time |
| 3. Red clamp | On the positive (+) terminal | Clamping the plastic terminal cover instead of metal |
| 4. Black clamp | On negative (−) or bare engine or chassis metal | Using a painted bracket that doesn’t conduct well |
| 5. Power on | Press the power button and wait for the Boost light | Jumping straight to Manual Override |
| 6. Start | Crank normally, then rest between tries | Cranking nonstop for long stretches |
| 7. Disconnect | Pack off, black clamp off, red clamp off | Letting the clamps touch while you put them away |
After the jump: what to do next
Getting the engine running fixes the immediate problem, not the reason the battery went flat. Once you’re moving:
- Drive for a while. A short trip to the store may not put back what the starter used. A longer drive gives the alternator more time to recharge the battery.
- Think about the cause. A dome light left on, a dash cam running in parking mode, or a cold snap can each drain a healthy battery. If none of those apply, the battery may be near the end of its life.
- Get it tested. Many auto parts stores will test the battery and charging system. If the battery won’t hold a charge, a jump starter only buys you time.
- Recharge the GB40. Plug it into USB as soon as you’re home, so it’s full for next time.
Where to keep it in the vehicle
I keep my GB40 where I can reach it without unloading the trunk, because the pack is only useful if it’s easy to grab. A glovebox, center console or seat-back pocket works. Avoid leaving it on the dashboard in direct sun, and check the storage temperature range printed in your user guide. Lithium packs hold their charge well, but check the charge LEDs every few months and top it up. A pack that sat half-empty all winter has fewer starts to give.
Where to buy
NOCO Boost Plus GB40 on Amazon
Related reading
FAQ
Which clamp goes on first with the NOCO GB40?
Plug the cable into the pack, then attach red to positive and black to negative or chassis ground, per NOCO’s guide.
Why won’t my GB40 turn on the Boost light?
It may not detect a battery below about 2V, or the clamps may be reversed. Check polarity, then consider Manual Override with care.
Is Manual Override safe?
It disables spark-proof and reverse-polarity protection, so it is safe only if you confirm polarity and keep the clamps apart.
What size engines can the GB40 start?
NOCO rates it for gas engines up to 6.0L and diesel engines up to 3.0L.
Can I charge my phone with it?
Yes, from its 5V/2.1A USB port.
Can the GB40 jump a 24V truck?
No. The GB40 is for 12V systems only. A 24V truck needs a jump starter rated for 24V.
Can I jump a car in the rain with the GB40?
The pack is rated IP65, but wet conditions make it harder to keep the clamps clean and apart. Shield the battery area if you can, keep the clamps from touching, and dry everything before you put it away.
One reply on “NOCO GB40 How to Use: Step-by-Step”
[…] you can pick the right charger and keep the pack ready. For the jump-start steps themselves, see my NOCO GB40 how-to-use guide and the full NOCO Boost Plus GB40 […]