Peak amps: the biggest number on the box
Peak amps is the most current a jump starter can push for an instant. No universal industry test defines it, so compare jump starters by the engine size the maker rates them for, not by this number.
Checked against sources on by the TrueAmps editorial team.
Even the makers say so
This is not our phrase. Lectron, which sells jump starters, writes that "peak amps are not governed by a universal industry testing standard" (Lectron's guide). A brand can measure it however it likes, and the number that ends up in a listing title is the one it chose to print.
Cranking amps are different. The same guide describes them as the current held for at least 30 seconds at 32°F while the voltage stays at 7.2 volts or more on a 12 volt system. That is a measurement you can repeat. NOCO's spec pages for the models on this site list peak current only.
Same battery, double the peak
NOCO's own spec pages show why the peak figure says little about capacity. The NOCO Boost Sport GB20 and the NOCO Boost Plus GB40 both hold a 24 Wh battery. NOCO rates one at 500 A and the other at 1,000 A, and gives them different engine ratings: 4.0 L gas with no diesel, against 6.0 L gas and 3.0 L diesel.
The engine rating is the manufacturer's statement of what the unit is for. It is the line to hold them to.
The same maker, rated two ways
NOCO lists the GB150 at 3,000 A today. Older reviews still describe it as a 4,000 A unit. The engine ratings, 9.0 L gas and 7.0 L diesel, are what we would hold the unit to, and they are the same figures NOCO publishes now. The GB150 record shows both sources.
NOCO's ratings, peak and engine
| Model | Peak A | Gas up to | Diesel up to | Battery |
|---|---|---|---|---|
| NOCO Boost Sport GB20 | 500 | 4.0 L | no | 24 Wh |
| NOCO Boost Plus GB40 | 1,000 | 6.0 L | 3.0 L | 24 Wh |
| NOCO Boost X GBX45 | 1,250 | 6.5 L | 4.0 L | 31 Wh |
| NOCO Boost X GBX55 | 1,750 | 7.5 L | 5.0 L | 46 Wh |
| NOCO Boost HD GB70 | 2,000 | 8.0 L | 6.0 L | 56 Wh |
| NOCO Boost X GBX75 | 2,500 | 8.5 L | 6.5 L | 74 Wh |
| NOCO Boost Pro GB150 | 3,000 | 9.0 L | 7.0 L | 88 Wh |
| NOCO Boost X GBX155 | 4,250 | 10.0 L | 8.0 L | 99 Wh |
How to read a jump starter listing
- Find the engine rating in liters, gas and diesel separately. If a listing gives only peak amps, look for the maker's own spec page.
- Look for the battery size in watt-hours. It tells you how much energy is stored; the peak figure does not.
- Look up the safety listing yourself. Here is how.
Questions people ask
What does peak amps mean on a jump starter?
The highest current the maker says the unit can deliver, for an instant. No universal industry test defines it, so one brand's figure cannot be compared directly with another's.
Is peak amps or cranking amps more important?
For choosing a jump starter, the maker's engine rating (gas and diesel liters) is the more useful number. Cranking amps describe current held for 30 seconds, which is closer to what starting an engine asks for.
How many amps do I need to jump start a car?
Choose by the engine size the manufacturer rates the unit for rather than by amps. For example NOCO rates its 1,000 A GB40 for gas engines up to 6.0 liters and diesel up to 3.0 liters.