A fully drained NOCO Boost Plus GB40 takes roughly three hours to recharge from a 2-amp USB charger, about six hours from a 1-amp charger, and around twelve hours from a 0.5-amp computer port, according to NOCO’s GB40 specifications. The pack stores 24 watt-hours in its lithium battery and charges through a 5-volt, 2.1-amp Micro-USB input, so the speed of the wall adapter you plug into decides almost everything about how long you wait.
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I own a GB40 and keep it in my vehicle, so recharging it after a jump or a long road trip is part of my routine. This guide pulls together NOCO’s published charging figures, explains what the charge lights mean, and walks through worked examples so 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 review.
GB40 charging specs
| Item | NOCO figure |
|---|---|
| Internal battery | Lithium-ion, 24Wh |
| Charge input | Micro-USB, 5V / 2.1A |
| USB output | 5V / 2.1A (USB-A) |
| Charge time at 0.5A | About 12 hours |
| Charge time at 1A | About 6 hours |
| Charge time at 2A | About 3 hours |
| Peak jump current | 1,000A, 12V |
| Starts per charge | Up to 20 |
NOCO includes a USB cable in the box but not a wall adapter, so the charger you pair it with matters. Any standard USB-A wall adapter or car USB port will work; it just changes the time.
How to charge the GB40, step by step
- Disconnect the clamps. Unplug the jumper cable from the pack before charging. NOCO’s guide says the unit should not be charged while connected to a vehicle battery.
- Plug in the Micro-USB cable. The charge port sits on the end of the pack under a protective flap.
- Connect the other end to a USB power source. A 2A or higher wall adapter gives the fastest charge. Laptop ports and older car USB sockets often supply 0.5A to 1A.
- Watch the power-level LEDs. The four white LEDs show 25, 50, 75 and 100 percent. They blink as each step fills and stay solid once that level is reached.
- Unplug when all four are solid. Then close the port flap to keep dust and moisture out, which helps the pack keep its IP65 rating.
Worked examples: how long will it take?
The figures below are my estimates, built from NOCO’s 24Wh capacity and its published charge times. Real times vary with temperature, cable quality and how flat the pack is.
Example 1: Fully empty, 2A phone adapter
NOCO quotes about 3 hours at 2A. At 5V and 2A, the adapter delivers 10W. Dividing 24Wh by 10W gives 2.4 hours of pure energy transfer; the extra half hour or so is charging losses and the slower top-off near full (estimate). Plan on an evening or an afternoon, not a lunch break.
Example 2: Half-charged, 1A car USB port
With two of four LEDs lit, roughly 12Wh remain to refill. NOCO’s figure is about 6 hours from empty at 1A, so half a charge should take about 3 hours (estimate). That suits a long highway drive, assuming your car’s USB port stays powered while driving.
Example 3: Topping off after one jump
NOCO rates the GB40 for up to 20 starts per charge, which means a single jump draws only a small share of the stored energy. If you see the pack drop from four LEDs to three, you are refilling about a quarter of 24Wh, or 6Wh. On a 2A adapter that is roughly 45 minutes (estimate).
| Starting level | 0.5A source | 1A source | 2A source |
|---|---|---|---|
| Empty (0 LEDs) | ~12 h | ~6 h | ~3 h |
| 25% (1 LED) | ~9 h | ~4.5 h | ~2.25 h |
| 50% (2 LEDs) | ~6 h | ~3 h | ~1.5 h |
| 75% (3 LEDs) | ~3 h | ~1.5 h | ~45 min |
Times in the table are estimates scaled linearly from NOCO’s empty-to-full figures. Lithium packs often charge a little slower near 100 percent, so the last LED can take longer than the others.
Choosing a charger
Because the GB40 input tops out at 5V and 2.1A, a high-wattage USB-C fast charger will not make it charge faster. A basic 2.4A USB-A adapter reaches the pack’s maximum. If you only have USB-C chargers, a USB-C to Micro-USB cable or adapter works, though the pack will still draw only 5V.
| Power source | Typical output | Expected GB40 full charge |
|---|---|---|
| Laptop USB-A port | 0.5A (USB 2.0) to 0.9A (USB 3.0) | ~7–12 h (estimate) |
| Older car USB socket | 0.5–1A | ~6–12 h (estimate) |
| 12V car USB adapter, 2.4A | 2.1A+ | ~3 h |
| Wall adapter, 2A or more | 2A+ | ~3 h |
| Power station USB-A port | Usually 2.4A | ~3 h |
That last row is handy for campers: a portable power station like the ones in my EcoFlow DELTA 3 Max review can refill the GB40 without dipping meaningfully into its capacity. 24Wh is a small fraction of even a 256Wh unit, before conversion losses.
Using the GB40 as a power bank
The GB40’s USB-A port puts out 5V at 2.1A, enough to charge a phone. Every watt-hour you take from it, though, is a watt-hour you can’t use for starting. A typical phone battery holds somewhere around 12 to 19Wh, so one full phone charge could use a large share of the pack’s 24Wh (estimate). If you rely on the GB40 for jump-starts, top it back up after using it as a phone charger.
Keeping it charged in storage
- Check monthly. Press the power button and look at the LEDs. Recharge whenever it drops below three LEDs so it’s ready when needed.
- Recharge after every use. NOCO recommends recharging after each jump.
- Mind the temperature. NOCO lists a charging range of 0°C to 40°C (32°F to 104°F). Charge it indoors in winter rather than in a freezing car.
- Store it in a moderate spot. A glovebox or center console is fine for most climates; on very hot days, a shaded spot or the trunk is gentler on lithium cells.
For broader background on battery capacity math, my guide on how long a 100Ah battery lasts uses the same watt-hour logic at a larger scale.
GB40 vs a larger jump starter on charging
Bigger packs store more energy and generally take longer to refill unless they accept faster input. For comparison, my Auxbeam 3500A jump starter review covers a larger unit with an air compressor. The GB40’s advantage is that its small 24Wh battery refills fully on an ordinary phone charger in an afternoon.
A charging timeline before a trip
If the GB40 has been sitting for a while, this simple plan makes sure it’s full when you leave:
| When | What to do | Why |
|---|---|---|
| The night before | Press the power button and count the LEDs | Tells you how much charging is needed |
| Same night | Plug into a 2A wall adapter | Reaches full in about 3 hours from empty |
| Morning | Confirm all four LEDs are solid, then unplug | A full pack gives the most starts |
| During the trip | Top up from a car USB adapter after any jump | Restores the small share one start uses |
Why the GB40 might charge slowly
- Low-current source. Laptop ports and some car sockets give 0.5–1A, which turns a 3-hour charge into 6–12 hours.
- Thin or long cable. Some cheap Micro-USB cables can’t carry 2A without a big voltage drop. Use the cable NOCO includes, or a short, good-quality replacement.
- Temperature. NOCO’s charging range is 32°F to 104°F. A pack charging in a cold garage or a hot car may charge slowly or not at all.
- Shared adapter. On a dual-port adapter, a phone on the other port can lower the current available to the GB40.
Since the pack only holds 24Wh, refilling it from a power station also costs very little: about 28Wh including conversion losses (estimate), around 11% of a 256Wh station.
FAQ
How long does the NOCO GB40 take to charge?
About 3 hours from empty on a 2A USB source, 6 hours on 1A and 12 hours on 0.5A, per NOCO.
Does the GB40 come with a wall charger?
It comes with a Micro-USB cable. You supply the USB wall or car adapter.
Can I charge the GB40 with USB-C?
Yes, using a USB-C to Micro-USB cable. Charging speed stays capped at the pack’s 5V/2.1A input.
How do I know it’s fully charged?
All four white power LEDs stay solid instead of blinking.
Can I leave it plugged in?
NOCO’s guide does not call for constant charging. Unplug once it reaches full and check it monthly.
How many jumps does a full charge give?
Up to 20 starts, according to NOCO, depending on the engine and conditions.
Can I charge it in the car?
Yes, from a car USB port or 12V USB adapter, ideally while the engine is running and the temperature is between 32°F and 104°F.
Why are the GB40’s LEDs blinking while it charges?
A blinking LED shows the level that’s charging right now. Each LED goes solid once its 25% step is full.
Bottom line
The GB40 is easy to keep ready: plug its Micro-USB port into a 2A adapter for about three hours and it’s full. Check the LEDs once a month, recharge after every jump, and skip the fast USB-C charger since the pack won’t use the extra power. You can find the GB40 on Amazon here.
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