Choosing the Best Jumper Pack: A Comprehensive Guide

How to choose the best jumper pack: What the specs really mean

With numerous options available on the market, choosing the best car jumper pack can be daunting. This article provides a comprehensive guide on what to look for when selecting a car jumper pack to ensure you make an informed decision. Particularly what the specifications mean when choosing the best jumper pack for your needs.

Assessing Your Needs

Jumper packs with lots of features are usually the lowest-quality units

Don’t get dazzled by jumper packs sporting cool features like an air compressor, USB ports, power ports, an AC inverter, or a spotlight/emergency light. Some of those units sell for less than $100. However, they’re garbage. They have a small battery that may run the compressor for a few minutes or power your phone in an emergency. But they won’t start your car when you need it most in winter. So, skip the fancy features and concentrate on the jumper pack’s ability to start your car. If you want an air compressor, buy a plug-in unit. They’re cheap.

Start by choosing the battery chemistry

Jumper packs can be fitted with an AGM, gel-cell lead-acid, or a lithium battery. Each type has pros and cons.

The advantages and disadvantages of a lead acid jumper pack battery

Pros:
• High power for a low price— Lead acid batteries provide a lot of power for an affordable price
• Easily replaceable— All jumper pack batteries have a limited lifespan. However, not all battery types are replaceable. AGM or gel-cell lead acid batteries are the easiest to obtain and replace.

Cons:
• Lead acid batteries have a higher self-discharge rate compared to lithium batteries. So you’ll have to recharge the jumper pack more often, usually every 6 to 8 weeks.
• Weight— Lead acid batteries are heavy and bulky. They won’t fit in your glove box and usually have to be stored in the trunk.

The advantages and disadvantages of a lithium jumper pack battery

Pros:
• Lower self-discharge rate— Lithium batteries hold their charge much longer than lead acid batteries, so they don’t require recharging as often. However, the manufacturers’ 1-year claims are misleading. See below for more details on charge life.
• Lighter and smaller than lead acid jumper packs— You can store a lithium jumper pack in your glove box, and it’s much lighter than a comparable output lead acid jumper pack.

Cons:
• More expensive than lead acid for the same power.
• You can’t replace the battery on the inexpensive jumper packs. They’re considered throw-away items. However, the batteries in the pro-grade models can be replaced for less than the cost of a new unit.

Summary: Inexpensive lithium jumper packs work, but they don’t last long and are considered throw-away items. The pro-grade lithium packs are of much higher quality and can be rebuilt. But they cost more than twice the price of the cheap packs.

What do the electrical specs mean, and how big of a jumper pack do you need?

Peak amps is a meaningless term—ignore it

Companies like to fool you with huge peak amp numbers. However, there are no industry standards for measuring peak amps. Because there’s no industry standard, comparing one unit’s peak amps to another is worthless. Besides, you want a battery that outputs power for longer than the short (millisecond) period used to measure peak amps.

Here are the electrical specs that mean something when buying a jump starter

• For lead acid jumper packs, compare the unit’s CRANKING AMPS or STARTING AMPS

CRANKING AMPS— Cranking amps (CA) refers to the number of amps a battery can output at 32°F (0°C) for 30 seconds while maintaining at least 7.2 volts.
STARTING AMPS— Starting amps is defined as the amount of amps a battery can output at 72°F for 30 seconds

• For lithium jumper packs, compare the unit’s STARTING ASSIST AMPS.

STARTING ASSIST AMPS— Since lithium jumper packs can’t be used to crank an engine for more than 5 seconds. the other rating terms can’t be used. Instead, the term STARTING ASSIST AMPS is used. Starting assist is defined as the number of amps the jumper pack can deliver for 5-seconds at 32°F.

NO OTHER RATING IS RELEVANT

Lithium jumper packs must have a UL listing or be UL-compliant

Lithium packs can be dangerous when used and can self-ignite if left in hot trunks. If you’re buying a lithium pack, make sure the unit is listed as UL 2743 or UL compliant. To prevent fires, it must comply with UL 2743

Next, consider the unit’s operational features

• Cable length— Manufacturers cut costs by installing short cables. Cheap units have 8″ cables, while the better units have up to 40″ cables. Short cables may limit your ability to reach a good ground connection point.

• Clamp style is important— Inexpensive packs have small clamps that often don’t fit on the battery terminals. In other words, cheap clamps don’t stay in place. Look for a pack that has standard-size clamps that’ll stay in place on the battery terminal

A note about phony peak amp ratings

Most of the cheap jump starters try to impress you with their peak amp rating. As mentioned earlier, there’s no industry standard for peak amps. So, each company can make up its own test protocol. In other words, a company can measure peak amps for 5 milliseconds versus 5 seconds.

Why do some jumper pack companies only list peak amps??

Look at this quote from the CTO of NOCO;

“For years, brands have used peak amperage as a way to differentiate its power output. The downside, though, with peak amps is that it provides little in the way of actual starting power and can often mislead consumers.”—Rick Stanfield, NOCO’s Chief Technology Officer

Ironically, NOCO jumper pack products are only rated in peak amps!

A note about lithium battery discharge rates

Lead-acid battery discharge rate

• Lead-acid batteries self-discharge at the rate of up to 1% per day, depending on the storage temperature. They self-discharge faster in hot weather and slower in cold weather. That means they must be recharged about once every 6 to 8 weeks. If you leave a lead-acid jumper pack in your car for the entire winter, it’ll likely be dead when needed. Worse yet, deeply discharged lead-acid batteries form sulfate crystals that can destroy the battery if left in a discharged state long enough. In other words, charge it or lose it.

Lithium battery discharge rate

• Lithium batteries, on the other hand, hold a charge much longer. But there are some caveats to that. Lithium batteries self-discharge in large drops. After 30 days, most lithium batteries drop to about 70% of their charge. Within six months, they drop to 30% and stay at that level for about a year. If you leave a lithium starter pack in your car for the entire winter without recharging it, chances are you’ll only have about 50% charge.

Some lithium jumper pack companies claim their products will hold their charge for over a year. That’s true but highly misleading since the charge level will be 50% or less within 6 months.

Lead-acid versus lithium battery replacement costs

A replacement battery for a beefy lead-acid style jumper pack costs about $60.

Here are the safety features your lithium jumper pack must have:

• Reverse Polarity Protection— to protect your car AND the jump starter in case you hook up the cables backward.
• Backfeed Protection— to protect the battery from high voltage and amps once the dead vehicle starts and its alternator starts pumping out power.
• Overheat Protection— to prevent the lithium battery from starting on fire when jumping and when being recharged.
• Over Voltage Protection— to protect the lithium battery from high voltage damage once the dead vehicle starts up
• Under Voltage Protection— to prevent damage to the lithium cells if you try to jump-start when the jumper battery is below minimum voltage.
• Short Circuit Protection— to prevent the lithium battery from starting of fire if you accidentally touch the cable clamps together.
• Proper Connection Verification
• Low Voltage Override

Lithium Jumper packs have limited cranking times for safety reasons

Because high heat can start a lithium battery on fire, you can only crank the engine for a maximum of 6 seconds when using a lithium starter pack. If the engine doesn’t start in 6 seconds, you must stop and let the lithium battery cool for at least three minutes. Then, you can try again for another 6 seconds. You can only repeat this process a total of four times. Then, you must recharge the jumper pack.

Look for these safety features in a lithium  jumper pack

• UL 2743 Very few jumper packs have passed the new UL 2743 standard. If you’re in the market for one, look for the UL 2743 seal on it.

• Short circuit protection — This one is pretty simple. The battery pack shut off if you accidentally touch the positive clamp to the negative clamp.
• Reverse polarity shutdown — The best battery packs prevent current flow if you’ve attached the cables to the wrong posts. This is a critical feature, and you shouldn’t buy a starter pack without it.
• Over-voltage — Once the engine starts, its alternator will start charging the battery and your jump starter immediately. Alternator output can be as high as 15.5 volts. That voltage isn’t a problem for jumper packs equipped with lead-acid batteries, but it IS a MAJOR problem for battery packs fitted with a Lithium battery. That high voltage can cause a lithium battery to start on fire or even explode. If you’re buying a Lithium battery jumper pack, over-voltage protection is a MUST.
• Over-current protection — Over-current protection is similar to over-voltage protection. It prevents the jumper battery from overheating based on a high amperage output from the car’s alternator. Here’s why that’s important. These starter packs are designed to recharge at home with a low current (amps) power supply. Recharging at a low current prevents damage and ensures long battery life. The power supplies are designed to charge at around 2-5-amps maximum. Once you start the engine, a car’s alternator can easily output 30-60 amps, depending on the engine’s RPM. No jump starter can handle that recharging amperage for long without damaging the battery or starting a fire. That’s why many jumper pack companies state that you must remove the pack IMMEDIATELY after the engine starts. The better packs still say that in their instructions, but they also limit the possible damage by shutting down the pack if alternator amps are too high.

• Over-temperature protection — When you attach a starter pack unit to a dead battery, you’re instantly draining the starter pack battery. Since lead-acid and lithium batteries produce electricity through a chemical reaction, rapid power production creates heat—lots of it. High heat can permanently damage a lead-acid battery. However, high heat in a lithium battery can cause it to explode. The best jumper packs prevent that possibility by automatically shutting off the pack if internal temperatures exceed a set value.
• Over-charge protection — This feature allows you to leave your jumper pack connected to the recharging power supply without worrying about battery damage due to overcharging. The power supply/charger circuit monitors the battery’s state of charge and shuts off the charger when it’s full.

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

Look at the jumper starter storage specs

If you think you can leave your jumper pack in the trunk when it’s -30F and expect it to work, think again. Lead-acid and lithium jump starters make power through a chemical reaction. Chemical reactions slow dramatically in cold weather. In most cases, you’ll see that lithium jump starters can’t be stored at temps below freezing. What does that mean for you? It means you’ll have to take it inside when you’re at home or work, OR you’ll have to warm it up before you use it to jump another vehicle. This is one area where lead-acid jumper packs perform better than lithium jump starters.

Clore JNC345

Clore automotive JCN345 lithium jump starter. 550 Start Assist Amps. 40″ cables

($40 on Amazon)
550 Starting Assist Amps (no peak amp listing)
6-gauge 40″ cable length with full size clamps
UL 2743 compliant

Link to the Clore JNC345 spec sheet

©, 2015 Rick Muscoplat