What Size Jump Starter Do I Need?

The short version

The rule behind the table: buy for your engine, then go one class bigger if your winters are genuinely cold. Everything below explains why.

Why "peak amps" is a slippery number

There is no industry standard for how jump-starter makers measure peak amps. One brand's 1,000A pack will out-crank another brand's 3,000A pack, and both numbers are "true" by their own test. The useful number is the engine rating the manufacturer publishes — "gas up to 6.0L, diesel up to 3.0L" — and the brand's reputation for being honest about it. NOCO's ratings are conservative; many budget brands' are optimistic. That's why a 1,000A NOCO and a 2,000A budget pack are often the same real-world tool.

• ▸1,000A class — starts four- and six-cylinder gas engines; fine for most commuter cars. Glovebox-sized.
• ▸2,000A class — V8 gas, light diesels, and the margin a V6 wants at 0°F. Door-pocket-sized.
• ▸4,000A class — heavy-duty diesels, RVs, farm and construction equipment, plow trucks. Under-the-seat-sized.

What the engine actually needs

A starter motor draws a large inrush current for a fraction of a second, then a lower cranking current while the engine turns. Bigger engines, higher compression (diesels), and thicker oil all raise both. A 2.0L four-cylinder at 70°F might crank on 150–250 amps; a 6.7L diesel at -10°F can pull several times that, for longer. The jump starter has to supply that on top of whatever the dead battery can't — which in a truly dead battery is all of it.

Cold: the factor everyone forgets

Cold hurts twice. Your car's battery delivers roughly a third less cranking power at 0°F than at 80°F while the engine needs up to twice as much to turn over through thick oil — that's why batteries die in January. But cold also hurts the jump starter: lithium packs lose capacity and output as they get cold, and most are rated only to about -4°F. A 1,000A pack that's been sitting in a frozen trunk is not a 1,000A pack.

• ▸Keep the pack in the cabin, not the trunk. In deep-cold country, bring it inside overnight.
• ▸Buy one class up if 0°F mornings are routine. The margin is what makes it work on the first try.
• ▸If the pack is cold and the car won't crank, warm the pack in your jacket for ten minutes and try again — it often works.
• ▸Top it off every 2–3 months. Lithium self-discharge is slow, but a pack at 30% in the cold is useless.

Lithium vs. lead-acid

Nearly every jump starter sold today is lithium: light, compact, holds a charge for months, and doubles as a USB power bank. The old-style lead-acid "jump box" — the Clore JNC660is the classic — still has a place. A sealed AGM battery delivers sustained cranking current without the voltage sag a small lithium pack shows on a long crank, it works in any temperature you'd be outside in, and it has four-foot cables that reach a truck or trunk-mounted battery. The cost is 18 pounds and the need to recharge it every few months. For a shop, farm, or fleet truck it's still the right tool; for the family car, buy lithium.

Features that matter (and ones that don't)

• ▸Spark-proof, reverse-polarity-protected clamps. Non-negotiable. Cheap packs without them are how you fry a car's electronics or yourself. Every pack we recommend has them.
• ▸A manual override / "boost" button for batteries so dead (below ~2V) the pack can't detect them. Real scenario after a week with a dome light on.
• ▸A bright flashlight with SOS. It'll be your roadside light.
• ▸USB-C power delivery — faster recharge and a useful power bank. Nice, not essential.
• ▸12V output for a tire inflator. Useful in winter when pressure drops.
• ▸Built-in air compressors — usually slow, and they drain the reserve you need to start the car. Buy a separate inflator.

How to jump a car with a jump starter, safely

• ▸Turn the car off — ignition, lights, blower, everything.
• ▸Clamp red to the positive (+) post (or the marked jump point under the hood on cars with the battery in the trunk).
• ▸Clamp black to a bare metal ground — an engine bracket or the designated ground point — or, if that's not possible, the negative (−) post. Smart clamps make this forgiving, but ground is the safer habit.
• ▸Turn the pack on. Wait for the ready light (or press the override if the battery's fully flat).
• ▸Crank for no more than ~5 seconds at a time. If it doesn't catch, wait 30–60 seconds — this lets the pack recover and the starter cool — and try again. Most packs allow several attempts.
• ▸Once running, remove black first, then red. Let the engine run 20+ minutes to recharge the battery — then get the battery tested; a jump is a symptom.

Our picks by class

• ▸1,000A: NOCO Boost Plus GB40 — the glovebox standard.
• ▸2,000A: NOCO Boost HD GB70 (buy-once) or GOOLOO GP4000 (budget).
• ▸4,000A / diesel: NOCO Boost X GBX155, or the lead-acid Clore JNC660 for a shop.

See the full jump starter rankings, or run the winter checklist to see where a jump starter fits in your whole kit.