Peak amps

Jumper pack peak amp rating

Lots of people rely on jumper pack peak amp rating. That’s a HUGE mistake because peak amps really isn’t a good indicator of the jumper pack’s ability to start your engine. From Jim O’Hara at Clore/Solar “Peak amps do start engines.” Jim’s right. There is NO industry-standard test for peak amps. It can mean anything the jumper pack manufacturer wants it to mean. So, it’s actually a meaningless term.

Battery ratings require time and temperature standards

To properly rate a battery’s jumping ability, you have to test it at an industry defined temperature, for an industry defined time period, with an industry defined maximum drop in voltage. Here’s the definition of cranking amps:

Cranking amps definition

Cranking amps (CA) refers to the number of amps a battery can output at 32°F (0°C) for 30-seconds while still maintaining at least 7.2 volts. The reason cranking amps is more important than peak amps is that people usually use a jumper pack to start their car in cold weather. Batteries produce power through a chemical reaction and that reaction slows when it’s cold. So you want a rating that’s based on a set temperature, which peak amps don’t have.

In addition to temperature, you also want to know how long a battery can output the specified number of amps. Think about, what good is a battery that puts out more amps but for such a short period of time that it can’t start your engine.  Finally, when the battery voltage drops below a certain point, it can no longer operate the starter motor. That’s why cranking amps cover total amp output at a set temperature, for a set period of time, all while maintaining a voltage above a set minimum.

Cold cranking amps (CCA) is like CA except that the rating is based on amperage output at 0°F (-17.8°C).

Peak amps are meaningless

So if a jumper pack manufacturer says their pack puts out 900 peak amps, do we know how the test was conducted? Do we know how long the test was for? Do we know what battery pack voltage fell to during the test? If not, the peak amp term means nothing. millisecond?

You can’t even use peak amps to compare one brand of jumper pack to another since each manufacturer’s testing method may be different. That makes jumper pack peak amp claims even more dubious.

One manufacturer’s 1,300 peak amp battery pack may not start your engine while another brand rated at 800 peak amp might.