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How Does a Portable Jump-Starter Work?

Jumper cables affixed to a car battery for use with a portable jump-starter.

Having a portable jump-starter in your car can mean the difference between being stranded and making it to your destination safe and sound during the winter months. These marvels of modern technology not only replace jumper cables, but also eliminate the need to flag down a passing motorist the next time your battery drains to the point where your engine won’t turn over.

How do these jump-starters work? Let’s take a quick look at this useful technology.

What’s Inside the Box?

The design of a portable jump-starter is very simple. Each is, at its core, a battery inside a case that incorporates a handle, a charging port and a pair of alligator cables. These cables can be attached to your vehicle’s own battery terminals (or a positive battery terminal and a ground) in order to provide enough juice to turn over your engine.

Not All Batteries Are the SameNBC 85924

You may have noticed that there are both large and small form factors when it comes time to shop for a portable jump-starter. This is tied directly to the type of battery the device uses to jump your car.

Larger units are built around a battery that shares its basic chemistry with a traditional automobile battery. Its large size allows it to offer excellent cold cranking amperage (CCA) when jump-starting a vehicle. You’ll need at least 150 CCA to start a compact car, but larger vehicles — or colder weather — can require as much as 450–600 CCA to get things going.

Smaller designs make use of lithium-ion batteries, which are similar to the type of energy storage units you would find in a modern smartphone or other mobile device. Despite their more modest dimensions, there are lithium-ion designs that can deliver the CCAs needed to jump a large displacement engine, too.

Which Is Better?

It may seem intuitive that the bigger the battery, physically, the more amperage it can send to your car. In reality, however, smaller lithium-ion portable jump-starters still offer excellent energy capacity, providing multiple starts between charges.

Some lithium-ion units can even handle big V8 engines in the coldest weather, but a larger, standard battery design is usually the better choice in such situations. If you don’t need more than 300 CCA, then lithium-ion and standard battery options will be comparable.

A final word on portable jump-starters: Many of these devices also offer extra features such as flashlights, USB charge ports, trickle-charge capabilities (for maintaining a car battery while parked) and even integrated air compressors. If you’re looking for more than just a charger, ensure that the capabilities of the units you’re considering meet your vehicle’s specific needs.

Check out all the tools & equipment available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on a portable jump-starter, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.


Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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