As an Amazon Associate I earn from qualifying purchases. Links to Amazon on this page are affiliate links.
Peak amps: the number you cannot compare
Updated
Peak amps is the highest current a pack can push for a brief moment. Each brand decides how to measure that moment. Car batteries have shared cold cranking amp tests. Lithium jump starter listings do not show one. So the amp number works only inside one brand's lineup, not across brands.
The proof is on the listings
Each listing we read gives headline amps and the largest engine the maker says it starts. Divide one by the other:
| Jump starter | Headline amps | Maker diesel rating | Amps per diesel liter |
|---|---|---|---|
| NOCO Boost GB40 | 1000 | 3.0L | 333 |
| NOCO Boost GBX75 | 2500 | 6.5L | 385 |
| GOOLOO GP4000 | 4000 | 10.0L | 400 |
| GOOLOO A3 | 3000 | 6.5L | 462 |
The GBX75 and the A3 claim the same 6.5 liter diesel. One says 2500 amps and the other says 3000. That is 500 amps of difference for the same stated job. On the gas side the spread is wider, from 125 amps per liter on the GB20 to 333 on the A3.
During our search we also read a listing claiming 6000 amps and diesel engines up to 12.0 liters from a pack listed at under 5 pounds. It gave no test method for the amp number and showed no owner review summary, so we left it out.
What to read instead
- The engine rating in liters. Gas and diesel, from the maker. Use the size picker to add cold weather headroom.
- The safety clamps. Look for reverse polarity protection and spark-proof clamps by name. All five of our picks list reverse polarity or reverse connection protection.
- A boost or override mode. Smart clamps look for battery voltage before they send power. A fully dead battery can read too low to detect. The GBX75 listing says this happens under 3 volts, and its manual override forces power on. The GOOLOO picks call this the BOOST button. Override turns off some protections, so check the clamps twice and follow the manual to the letter.
- The warranty. On the listings we read, NOCO gives 1 year and GOOLOO gives 18 months.
What mAh does not tell you
Milliamp hours tell you how much energy the pack stores, which matters for charging phones. It does not tell you how hard the pack can push for the few seconds a start takes. A big mAh number and a big amp number are both labels. The liters rating is the claim you can hold the maker to.