Jump Starters
How to charge a jump starter
The charging part is easy. The habit is what people get wrong, and it is the difference between a working tool and a paperweight.
Disclosure: we earn a commission if you buy through the Amazon links on this page, at no extra cost to you. Commission never decides a verdict or a ranking position — read our editorial policy and affiliate disclosure.
How we assessed these: procedures here follow the general sequence manufacturers publish for lithium jump packs. Always follow your own pack's and vehicle's manuals where they differ — designated jump points vary by vehicle.
Short answer
Charge from the input your pack specifies — USB for compact packs, a 12 V fast-charge input on larger ones. A NOCO GB40 takes about three hours from a powered USB port at 2.1 A; a GB70 about three hours at 12 V / 3 A. Top up every three months whether you have used it or not.
Charging times and inputs, as published
| Pack | Capacity | Charging input | Published time |
|---|---|---|---|
| NOCO GB40 | 24 Wh | USB, 5 V / 2.1 A | About 3 hours |
| NOCO GBX45 | 31 Wh | USB-C Power Delivery, up to 20 V / 3 A | Not published as a single figure |
| NOCO GB70 | 56 Wh | 12 V / 3 A fast charge | About 3 hours |
Figures from NOCO's specification pages. Where a manufacturer does not publish a single charging time — because it varies with the source's output — we leave it blank rather than inventing one.
The input matters more than the time. A pack that charges from USB-C Power Delivery, like the GBX45, charges from the brick you already own — which in practice is the difference between a pack that gets topped up and one that does not. A pack with a proprietary barrel connector needs its own charger, and that charger is the thing that goes missing.
The habit that actually matters
Every three months, whether you used it or not. Lithium self-discharges slowly — much more slowly than lead-acid — but it does self-discharge, and a pack sitting at 40% is a pack with 40% of the margin you paid for. Quarterly is a rhythm people can keep; tie it to the clock change and you will remember two of the four.
Always after use. A pack that started your car has spent real energy, and the next problem may be a week away.
Before any trip you are relying on it for. Especially before winter, and especially after a hot summer.
Can you charge a jump starter from the car?
Yes, if the pack supports a 12 V input — the GB70's fast-charge input is exactly this. It is genuinely useful on a long drive: you can bring the pack back up while you travel rather than waiting for a wall outlet. Two conditions: the engine should be running, so you are drawing from the alternator rather than the battery you are trying to protect, and the 12 V socket needs to be live with the ignition on.
For USB-only packs, any USB source works, including a laptop — it will just be slower at lower current. If the pack accepts USB-C Power Delivery, a laptop-class brick will be meaningfully faster than a phone charger.
Charging without the original charger
For USB and USB-C packs, that is a non-issue — use any compliant cable and source. For packs with a proprietary connector, contact the manufacturer for a replacement rather than improvising with a bench supply. Feeding a lithium pack an unregulated or mismatched supply is the one genuinely dangerous thing on this page.
Signs the pack needs replacing rather than charging
- It will not reach full charge, or the indicator cycles without completing.
- It reaches full and drops quickly with no use — capacity has gone.
- It gets hot while charging. Warm is normal; hot is not.
- The case is swollen or deformed. Stop using it, stop charging it, and dispose of it properly at a battery recycling point — never in household waste.
- It no longer starts an engine it used to start. Capacity loss is usually why, and it is not recoverable.
Packs that are easy to keep topped up
1. Easiest to keep charged
NOCO Boost X GBX45
NOCO · Best for travel and carry-on use
The travel pick: 1,250 peak amps at 2.16 lb with USB-C Power Delivery in and out, so it recharges from the same brick as your laptop.
Published specifications
- Peak amps
- 1,250 A source
- Internal battery
- 31 Wh lithium-ion source
- Gas engine rating
- Up to 6.5 liters source
- Diesel engine rating
- Up to 4.0 liters source
- Weight
- 2.16 lb (0.98 kg) source
- USB-C output
- Up to 20 V / 3 A Power Delivery source
- Water resistance
- IP65 with ports closed source
- Warranty
- 1-year hassle-free source
What works
- Lightest pack in the range at 2.16 lb, and 31 Wh means no airline paperwork
- USB-C Power Delivery both directions — one cable covers the pack, phone and laptop
- More gas headroom than the GB40 (6.5 L against 6.0 L) in a lighter body
What does not
- The IP65 rating only holds with the port covers closed — worth remembering in the rain
- The 4.0 L diesel ceiling is not enough for a full-size diesel pickup
Skip it if
Not the right pack for a diesel truck, and not the cheapest way to cover a small commuter — its premium buys packability, not amps.
#ad Affiliate link · We show no price here; Amazon shows the current one
Raw specifications: NOCO’s own page for the NOCO Boost X GBX45.
2. Fastest practical recharge
NOCO Boost HD GB70
NOCO · Best for diesel pickups and big v8s
The one to buy if you drive a diesel: 2,000 peak amps, a 6.0-liter diesel rating and 56 watt-hours, which is the smallest pack with real margin on a cold diesel.
Published specifications
What works
- The 6.0 L diesel rating covers the common 3.0 L and 6.7 L light-truck diesels with margin
- 56 Wh is still comfortably under the 100 Wh carry-on threshold, so it flies as hand luggage
- 12 V 15 A accessory output, and a 400-lumen light that is genuinely usable roadside
- 12 V / 3 A fast charge brings it back in about three hours
What does not
- 4.18 lb — noticeably heavier than the compact packs, and it wants a dedicated spot
- Overkill for a commuter four-cylinder; you are paying for headroom you will not use
Skip it if
Not the one to buy if you only ever start a four-cylinder commuter. Buy diesel headroom when you have a diesel.
#ad Affiliate link · We show no price here; Amazon shows the current one
Raw specifications: NOCO’s own page for the NOCO Boost HD GB70.
Key takeaways
- A GB40 charges in about 3 hours at USB 2.1 A; a GB70 in about 3 hours at 12 V / 3 A.
- USB-C Power Delivery packs get charged more often, because no special brick is needed.
- Top up quarterly regardless of use, and always after use.
- You can charge from the car's 12 V socket with the engine running.
- A swollen case means stop — recycle it, do not charge it.
How we sourced this
Every figure on this page came from one of the following. Where a manufacturer or regulator does not publish a number, we say so rather than estimate it.
Common questions
- How long does it take to charge a jump starter?
- NOCO publishes about three hours for the GB40 from a powered USB port at 2.1 amps, and about three hours for the GB70 using its 12 V, 3 A fast-charge input. A lower-current source takes proportionally longer, so charging from a laptop port will be slower than from a wall adapter.
- How often should I charge my jump starter?
- Every three months whether you have used it or not, and always immediately after use. Lithium self-discharges slowly but it does self-discharge, and a pack at partial charge has lost some of the margin you bought it for.
- Can I charge a jump starter in the car?
- Yes, if it has a 12 V input — larger packs commonly do. Run the engine while charging so you are drawing from the alternator rather than the battery you are trying to protect, and check that the socket is live with the ignition on.
- Does a jump starter have to be fully charged to work?
- No, but capacity directly determines how many attempts you get, and a partly charged pack has fewer. In cold weather each attempt costs more energy, so the margin a full charge gives you matters most exactly when you are least likely to have it.
More in Jump Starters
A jump pack is the one trunk tool that turns a tow truck into a five-minute inconvenience. This is how to size one, and which ones are worth the space.
Read next
Guide
How Long Does One Last?
Charge retention, starts per charge and total service life, separated out — plus the one factor that shortens all three.
Guide
Storage and Heat
Why a hot trunk permanently costs a lithium pack capacity, where to store it instead, and the one case where lead-acid genuinely wins.
Troubleshooting
Jump Starter Not Working
A symptom-by-symptom walk through the common failures, and how to tell a dead pack from a pack that is refusing to engage on purpose.
How to
How to Use One
The full sequence for a lithium jump pack, plus what to do when the first attempt does not work and when to stop trying.
Found something out of date, or a figure you can source better than we did? Tell us — corrections get read first. Our methodology explains how picks are made, and contact is one click away.