Rick's Free Auto Repair Advice

How to buy a jumper pack

How to buy a jumper pack

Every big box and auto parts store sells “jumper packs.” But many emergency and portable power packs masquerade as jumper packs. They may start a dead car, but only if the car’s battery is partially discharged. So you need to know how to buy a jumper pack.


I’ve interviewed all the big players in jumper packs at the 2019 AAPEX and SEMA shows and learned that some manufacturers are still pedaling B.S when it comes to jumper pack specs. Here’s what I heard and they’re all B.S.

“Our jumper packs stay charged for a year and a half.”

“You can keep our jumper pack stored in your trunk and it’ll start your car or truck.”

” We rate our jumper packs for peak amps because that’s all consumers understand.”

Jumper pack peak amp rating is meaningless

From Jim O’Hara at Clore/Solar “Peak amps do start engines.” Jim’s right. There is NO industry standard test to define what the term peak amps actually means. Since there’s no a””ccepted industry definition, it’s actually a meaningless term. 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.

What battery rating counts?

When you buy a car battery, it has a Cranking Amps (CA) rating. CA tests are standardized within the industry, so you can rely on that rating. The same holds true when it comes to jumper packs. Buy a pack based on its CA rating, not peak amps.

How many CA amps do you need? Well, if you’re trying to jump start a dead battery on a 4-cylinder engine, 200 CCA will do the job. If you’re starting a larger engine, look for a larger pack.

Cranking amps definition

Cranking amps (CA) refers to the number of amp 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 because people usually use a jumper pack to start their car in cold weather. Batteries produce power through 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 doesn’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 battery voltage drops below a certain point, it can no longer operate the starter motor. That’s why cranking amps covers 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).

What safety features should you look for in a lithium ion jumper pack?

Let’s cut to the chase here; lithium ion batteries have some important advantages over lead acid batteries. But they have some inherent drawbacks too. They can ignite if overcharged or drained at too high a rate. They can also ignite if recharged too quickly or at too high a rate. And, they can be damaged if you reverse the polarity when jump starting. So the lithium ion jumper pack you choose should have built in safety features to prevent fire and battery damage.

jumper pack, booster pack, how to jumpstart a car

This JNC660 jumper pack from Clore Automotive is rated at 425 Cold Cranking amps

How long does a jumper pack hold it’s charge?

Only one jumper pack manufacturer at AAPEX and SEMA told us the truth when I asked how long a charge would last on their jumper packs. That was Jim O’Hara from Clore. He recommends charging a jumper pack every 90 days. Here’s why.

It all comes down to battery basics

Charge a battery to 100% and then let it sit. I don’t care if it’s a lead acid battery or a lithium ion battery, it’s going to lose a significant amount of its charge within 90 days. However, if you use a lithium battery until it draws down to about 30% change and then leave it, it can stay at the charge for a year to a year and a half.

But most of the battery pack manufacturers I talked to at 2019 AAPEX and SEMA all said their battery packs would hold their charge for a year and a half. That’s really misleading.


©, 2015 Rick Muscoplat


Posted on by Rick Muscoplat


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