How Many Amps Do You Need in a Jump Starter?
2 lessons in this series, 6 min in total
- Peak vs Cranking Amps: Which Jump Starter Number Matters? 3 min read
- How Many Amps Do You Need in a Jump Starter? 3 min read
This guide draws on NOCO’s GB40 and GB70 data sheets, Clore’s JNC660 product page and manual, AAA Hudson Valley and Rick Muscoplat’s jump-pack buying guide. Read how we research.
Two terms in brief: peak amps are a burst figure each maker sets with no standard test, and cranking amps are the current held for 30 seconds at 32°F (0°C). The first lesson explains what peak and cranking amps mean.
Engine ratings by maker: gas vs diesel
Is 1000 amps enough to jump a car? It depends on whose 1000 amps, so the practical number is each maker’s own engine rating.
| Spec | NOCO Boost Plus GB40 | NOCO Boost HD GB70 | Clore JNC660 |
|---|---|---|---|
| Battery type | Lithium-ion, 24 Wh | Lithium-ion, 56 Wh | Sealed lead-acid |
| Peak amps | 1000A | 2000A | 1700A |
| Cranking amps | Not listed | Not listed | 425A |
| Gas engines | Up to 6.0L | Up to 8.0L | Not listed |
| Diesel engines | Up to 3.0L | Up to 6.0L | Not listed |
| Rated jump starts per charge | Up to 20 | Up to 40 | Not fixed |
“Not listed” means the item doesn’t appear in that maker’s documents for the unit.
Diesels need more. The GB40’s gas rating is twice its diesel rating, and Muscoplat warns against assuming a small glove-box pack will start a diesel. Going from 1000A to 2000A raises NOCO’s gas rating from 6.0L to 8.0L but doubles its diesel rating from 3.0L to 6.0L.
Clore gives no engine-size rating for the JNC660. Its manual says the unit has more than enough power to start most cars and that its main job is giving a weak battery an extra boost. The manual calls 10-30 starts per charge feasible.
Size it in three steps
- Find your engine size in liters. Check your owner’s manual or the specs for your model.
- Note whether it’s gas or diesel. Use the diesel rating for a diesel.
- Pick a unit rated above your engine, not right at the limit. Muscoplat advises leaving a reasonable margin for winter.
Here’s how the steps play out for a 6.0L engine. On gas, NOCO’s GB40 is rated for it, though right at its limit. On diesel, the GB40 covers only 3.0L and the GB70 tops out at 6.0L, so a pack rated for 6.0L gas can’t be assumed to start a 6.0L diesel.
Large diesel pickups need extra care. An engine over 6.0L is outside even the GB70’s diesel rating, so you’d need a unit rated for that displacement.
Add a winter margin
Cold hits both sides of a jump start. AAA Hudson Valley, citing AAA’s Automotive Research Center, says a car battery loses about 35% of its strength at 32°F (0°C) and about 60% at 0°F (-18°C), which is why a weak battery shows up in cold weather. AAA adds that starting the engine in the cold may take up to twice the normal current.
If you see winter mornings near 0°F (-18°C), plan for that morning, not an average one. A gas engine near the top of a pack’s rating, like a 5.7L V8 on a 6.0L-rated unit, leaves little room for a weak, cold battery. Stepping up one size gives you that margin.
The packs have limits too: NOCO says the GB40 and GB70 charge only above 32°F (0°C), and Clore says not to store the JNC660 below 50°F (10°C), which shapes the answer to can you leave a jump starter in your car. Both brands also say never to jump-start a frozen battery, one of the cases covered in when not to jump-start a battery.
Which of the three fits your engine
Pick by engine size and fuel first.
The GB40 suits gas engines up to 6.0L or diesels up to 3.0L, and it weighs 2.4 lb (1.1 kg) with clamps and accessories, per NOCO’s data sheet.
NOCO Boost Plus GB40
A compact 12V lithium jump starter. NOCO rates it at 1000A peak, for gas engines up to 6.0L (366 cu in) and diesel engines up to 3.0L.
Key specs
- 1000A peak
- Gas engines up to 6.0L, diesel up to 3.0L
- Compact 12V lithium
Paid link
View on Amazon (opens in a new tab)The GB70 suits gas engines up to 8.0L, diesels up to 6.0L, or a gas engine near 6.0L in a cold climate, with a 56 Wh battery rated for up to 40 starts per charge at 5 lb (2.3 kg).
NOCO Boost HD GB70
NOCO's larger lithium jump starter: 2000A peak, rated for gas engines up to 8.0L and diesel engines up to 6.0L.
Key specs
- 2000A peak
- Gas engines up to 8.0L, diesel up to 6.0L
- 12V lithium
Paid link
View on Amazon (opens in a new tab)The JNC660 suits buyers who want a published cranking rating: it is the only one of the three with one, 425 cranking amps alongside 1700 peak amps, with a sealed lead-acid battery, 46 in (117 cm) #2 AWG cables and a weight of 18 lb (8.2 kg).
Clore Jump-N-Carry JNC660
A heavy-duty 12V lead-acid jump starter from Clore: 1700 peak amps and 425 cranking amps, with 46-inch (117 cm) cables.
Key specs
- 1700 peak amps, 425 cranking amps
- 46 in (117 cm) cables
- 12V lead-acid
Paid link
View on Amazon (opens in a new tab)Look up your engine size and fuel type, then compare the two NOCO packs line by line in NOCO GB40 vs GB70.
Sources
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- NOCO GB40 data sheet (PDF)
- NOCO GB70 data sheet (PDF)
- Clore Automotive: JNC660 1700 Peak Amp 12 Volt Jump Starter
- Clore Automotive JNC660 operator’s manual (PDF)
- Rick’s Free Auto Repair Advice: How to Buy a Jumper Pack: What the Specs Really Mean
- AAA Hudson Valley: Cold Weather Is Hard on Your Car Battery
