Jump Starters
Peak amps vs cranking amps
The biggest number on the box is the one that matters least. Here is what each figure measures and which to buy on.
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How we assessed these: the figures on this page come from manufacturer specification pages and regulator publications, cited inline. Nothing here is estimated or restated from memory.
Short answer
Peak amps is the highest current a pack can deliver for an instant. Cranking amps is the current it can sustain while the starter actually turns the engine. Cranking current does the work, but almost nobody publishes it — which is why the engine rating in liters is the figure to buy on.
| Figure | What it measures | How useful |
|---|---|---|
| Peak amps | Maximum instantaneous current, measured over a fraction of a second | Marketing-grade. Not defined identically across brands, so not comparable between tiers. |
| Cranking amps | Current sustained for several seconds, which is what a starter motor actually draws | Genuinely useful — and rarely published on consumer jump packs. |
| Engine rating (liters) | The largest engine the manufacturer will stand behind the pack starting | The one to buy on. It already folds in everything the other two leave out. |
Why peak amps is the number you see
Because it is the largest. Peak current is measured over an interval so short that it tells you very little about turning an engine over for four seconds in February, but it produces the biggest figure to print on a box, so it is the figure that gets printed.
The deeper problem is that "peak amps" is not standardized the way a battery's CCA rating is. Automotive batteries have cold cranking amps defined by an industry test — a specified current at a specified temperature for a specified duration. Jump-pack peak amps has no such universal test, so a budget pack advertising 4,000 A and a major brand advertising 2,000 A may simply be measuring differently. Comparing those two numbers directly tells you nothing.
What the starter motor actually needs
When you turn the key, the starter draws a large inrush current for a fraction of a second, then settles into a lower but still substantial sustained draw while it turns the engine. A typical car needs that sustained draw for one to four seconds; a cold diesel needs longer, and needs it after the glow plugs have already taken their share.
So the demand curve is: a spike, then a plateau. Peak amps addresses the spike. The plateau is what actually starts the engine, and it is where an underrated pack fails — it engages, the engine turns slowly, and the pack gives up.
What to compare instead
- The published engine rating, for your fuel type. Gas and diesel ratings differ by roughly a factor of two on the same pack. Read the right column.
- Watt-hours. This is a real, standardized unit of energy. It determines how many starting attempts you get, and it decides whether the pack can fly. See mAh vs watt-hours.
- Peak amps within a single brand's range. Comparing a GB40's 1,000 A to a GB70's 2,000 A is meaningful, because one manufacturer measured both the same way. Comparing across brands is not.
- Whether the rating is warranted at all. A brand that publishes a specific engine rating has committed to something. A brand that publishes only a peak-amp figure has not.
One more figure worth ignoring
mAh. Milliamp-hours without a stated voltage is not a capacity — it is half of one. A pack advertising "20,000 mAh" is telling you nothing until you know whether that is at 3.7 V or 12 V, and the difference is a factor of three. Worse, on a pack you might want to fly with, it actively obscures the watt-hour figure that airline rules are written around.
Packs whose ratings you can check
1. 1,000 peak amps, honestly rated
NOCO Boost Plus GB40
NOCO · Best for most cars and small suvs
The default answer for a four- or six-cylinder car: 1,000 peak amps, 24 watt-hours, and light enough that it actually stays in the trunk.
Published specifications
What works
- 24 Wh sits far under the 100 Wh carry-on threshold, so flying with it needs no airline approval
- 2.45 lb and pocketable — the size that decides whether a tool is still in the trunk six months later
- IP65 enclosure, so a wet shoulder in the rain is not a problem
- Reverse-polarity protection means a backwards clamp does not spark
What does not
- 1,000 peak amps runs out of headroom above a 6.0 L gas engine
- The 3.0 L diesel ceiling rules out most modern diesel pickups
- 24 Wh is a small reserve — it is a jump starter, not a power bank substitute
Skip it if
Not the one to buy if you drive a diesel pickup or a big V8. You would be at the edge of its rating on a cold morning, which is exactly when you want margin.
#ad Affiliate link · We show no price here; Amazon shows the current one
Raw specifications: NOCO’s own page for the NOCO Boost Plus GB40.
2. 2,000 peak amps, honestly rated
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.
3. What a loose claim looks like
GOOLOO GT4000S
GOOLOO · Best for maximum claimed amps per dollar
A high-claimed-amp budget pack. Worth a look on price, but read the rating language closely — peak-amp claims in this tier are not stated the way the majors state them.
This manufacturer does not publish a full specification table for this model on its own site. Rather than repeat figures we cannot source, the assessment below is limited to what the product category and the retailer listing genuinely establish.
What works
- One of the cheapest routes to a large-engine rating
- Usually ships with a case, cables and a wall adapter in the box
What does not
- Budget-tier peak-amp claims are not directly comparable to a major brand's published rating
- Support and warranty handling is the usual weak point against NOCO or DEWALT
- Capacity is often quoted in mAh rather than watt-hours, which obscures airline legality
Skip it if
Not the pick if the pack is your only plan for a remote breakdown. For that, pay for a published rating and a warranty you can actually use.
#ad Affiliate link · We show no price here; Amazon shows the current one
Key takeaways
- Peak amps is an instantaneous figure with no universal test behind it.
- Cranking amps is what starts the engine, and consumer packs rarely publish it.
- The engine rating in liters is the one figure the manufacturer warrants.
- Compare peak amps only within one brand's range, never across brands.
- mAh without a voltage is not a capacity — look for watt-hours.
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
- What is the difference between peak amps and cranking amps?
- Peak amps is the maximum current a pack can deliver for an instant. Cranking amps is the current it can sustain for the several seconds a starter motor actually needs. Cranking current does the work, but it is rarely published on consumer jump starters.
- How many peak amps do I need to start my car?
- Rather than a peak-amp target, use the manufacturer's published engine rating. A pack rated at 1,000 peak amps is typically rated to start gas engines up to 6.0 liters, which covers most cars. Peak-amp figures are not comparable between brands.
- Why do cheap jump starters claim such high peak amps?
- Because peak amps has no standardized industry test the way a car battery's cold cranking amps does, so brands can define the measurement differently. A 4,000-amp claim from one brand and a 2,000-amp claim from another are not necessarily describing the same thing.
- Should I ignore peak amps entirely?
- Not entirely — it is useful for comparing models within a single manufacturer's range, since they were measured the same way. It is comparing peak amps across brands, and treating a bigger number as automatically better, that leads people wrong.
More in Jump Starters
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Guide
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mAh vs Watt-Hours
The conversion, worked through, plus why watt-hours is the only capacity figure that matters if the pack is ever going on a plane.
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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.