FAQs: Battery Jump Starters, All Your Questions Answered

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Battery jump starters are one of the most useful items any driver should carry. Flat batteries are one of the most common breakdowns in any car or truck.

But there’s a lot of mystery about portable jump starters… how do they work, what size do I need and so on.

Have a browse through these FAQs and find out a whole lot more about jump starter packs for your car or truck. And if you have any other questions, please ask in the Comments at the end of this post.

We’ve also done a comprehensive review on our NOCO Genius Boost GB70 Portable Jump Starter. Go here for more information.

How do battery jump starters work?

Portable or battery jump starters come with their own internal battery. They’re designed to provide a high current for a short amount of time, just like your car’s starting battery.

You simply connect the two clamps to the battery terminals, red to positive and black to negative. Press the On button on the jump starter, then start your vehicle.

Once the car starts, switch the jump starter off, disconnect the (red) positive clamp then disconnect the (black) negative clamp.

Note, they won’t charge your battery. They are designed only to provide the high current a car needs for starting.

Related questions
– How do I use a portable jump starter?
– How do I jump start a car without cables?

How is a battery jump starter charged?

The jump starter’s internal battery needs to be kept charged, so it’s ready for use. They’re charged using a mains (240VAC) plug or a USB plug, depending on the model.

How long does a portable jump starter stay charged before you have to charge it again?

A high quality jump starter will maintain its charge indefinitely. As a guide, if you haven’t used it for 6 months then check the charge level.

To give you an idea, the NOCO range will only lose 1 – 2% of its battery power per month if it’s not used. Look for a similar specification when buying.

What’s the best car battery jump starter?

The best battery jump starter is one that’s large enough to start your car! ☺️  See below for more details on how to size a jump starter. Generally, the more you pay the higher the quality.

Features to look for:

✔︎ Spark-proof. This is important, as lead-acid batteries (used in most vehicles) can give off explosive gases.

✔︎ Reverse polarity protection. This means if you connect the clamps to the wrong terminals, the jump starter will show a fault light and will not operate.

✔︎ Rechargeable from USB and 12V ports. Being rechargeable from mains power is also useful, but not necessary if it’s rechargeable from USB ports.

✔︎ Has an LED flashlight. This is priceless when you’re caught with a flat battery at night. And being LED, it won’t use much power. A flashing strobe function is also useful in an emergency. For example, if you’re broken down in a dangerous position at night, you can use this to warn other traffic.

✔︎ Has the ability to charge devices like phones from a USB outlet.

✔︎ Has a manual override feature which allows you to start batteries below 2 volts.

✔︎ Is lightweight and portable.

What size portable jump starter do I need?

The best way is to look at the top of your battery and find the Cold Cranking Amps rating, or CCA. It will have “CCA xxx” somewhere on the battery’s label (xxx will be a number).

The cold cranking amps (CCA) rating of a typical car battery.The CCA rating of a car battery should be on the battery’s label.

If not, have a look in the Electrical Specifications section of the vehicle’s Owners Manual or call your vehicle dealer or a battery sales outlet.

The CCA increases as the engine size increases, and diesel engines need a larger CCA rating than a petrol engine for the same engine size.

Also consider whether you might want something bigger than you need, in case you buy a larger vehicle in the future.

Once you’ve decided what CCA rating you need, choose a battery jump starter with a higher rating. This way, you can be sure it will start your car. Confusingly, the jump starter will be rated in Amps.

Say your battery’s rated at CCA 540. In this case, a jump starter rated at higher than 540A will be okay.

A NOCO Genius GB40 will start most cars. Just double-check the battery’s CCA rating against the jump starter’s amperage rating first (1,000A for the GB40).

Related questions
– How do you determine which portable battery jump starter to get for your car for emergencies?
– Which Noco Genius do I need?

Should you always keep jumper cables in your car?

Yes, you should always keep jumper cables or a portable jump starter in your car. Batteries have a tendency to fail at the least convenient moment… on a cold, rainy night in a deserted carpark or when you’re running late for that important meeting.

Should you buy jumper cables (also known as jumper leads) or a battery jump starter? The downside of jumper leads is you need a second vehicle to act as the starting vehicle.

Another consideration… many people are loathe to connect jumper leads to their vehicle, because jump starting has been known to damage the electronics in modern cars.

However, if you have a portable jump starter, then you’ll be self-contained. You don’t need someone to help you.

Do those portable jump starter battery packs really work?

Most definitely… if you buy a quality unit. We’ve used ours dozens of times now and it has worked faultlessly every time.

We did have a set of jumper leads, but wouldn’t even consider going back to them now. The portable jump starters are so quick and easy to use, plus they have a whole lot of safety features.

No more concerns about connecting them wrongly, accidentally causing dangerous sparks or damaging the vehicle’s delicate electronics. Plus, you get a whole lot of extra features… USB charging for your devices, a flashlight and emergency strobe, and no more messy tangles of jumper cables taking up storage space.

Go here for a wide selection of quality jump starters and accessories.

What’s the difference between a portable car battery charger and a portable car battery jump starter?

A car battery charger slowly restores charge to a flat battery. It uses low current to gradually charge the battery. This can take several hours.
Note: If you want to know more about portable battery chargers, go here.

Battery chargers runs through several charging stages, optimising the charge in the battery. When finished the battery will be fully charged (assuming the battery’s not faulty).

A portable car battery charger is simply a small charger you can easily pick up and carry with you.

A portable jump starter does not charge your flat battery. It simply provides the high level of current needed to start your car. The jump starter is designed to provide short bursts of very high current.

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8 thoughts on “FAQs: Battery Jump Starters, All Your Questions Answered”

  1. I bought a 2000 amp jump starter for my Pajero 3.2L Diesel.
    First time I needed to use it, even though it showed 100% charge, it wouldn’t turn the engine over. RAC said my battery needed replacing which I did. Enquired with manufacturer why jump starter didn’t work and to my surprise was advised that they didn’t work on failed batteries.
    So apparently only useful if good battery goes flat by leaving lights on etc, but no use if battery dies. I haven’t seen this mentioned on any advertising or documentation supplied with the unit or for that matter on any other brands. In future I won’t be going bush without a new battery, so probably wasted money buying the jump starter.

    • Hi Bernard,

      I’m not quite sure why the manufacturer would say this. That doesn’t sound right. What brand is it?

      We have 2x12V (24V system) batteries in our Isuzu truck. One was 100% dead and the other was almost dead. I attached one NOCO Genius GB70 to each battery and started the truck several times without issue.

      Does your jump starter have the function to override its safety features (reverse polarity protection, etc), so you can start a completely dead battery?

      You definitely shouldn’t need to carry a spare battery. That’s what the jump starter is for… to get you out of trouble (just as you thought when you bought it).

      Any half-decent jump starter will start your vehicle when the battery is dead.

      Cheers, Andrew

  2. I bought a Nexpow 2000 battery jump starter. When I connected to a dead car battery, it beeps and shows r sc. I tried to figure out what that means but no luck. Do you know? Does it mean that the starter won’t be able to start a totally dead battery? I couldn’t find a website or contact info for the battery pack.

    • Hi,

      You need a manual override button for when you need to jump start a completely dead battery. The Nexpow 2000 does not have this (very useful) feature.

      Cheers, Andrew

  3. Andrew, I’m thinking of using one of these jump starters as a high current source of 12v for my boat anchor winch (950w motor). It requires up to max of 80amps (varies from 10-80 with load) for about 2mins for a typical anchor raising. I have solar charging onboard with 12v outlets so I could easily charge from that I guess. Plus I’d have the flexibility to bring home for charging at the end of the day or weekend.
    If this will work, it will save me a ton of weight (and a little money) and eliminating a need to find another charging source for a 2nd battery. My boat is only small and light and the engine is a little outboard.
    What do you think?

    • Hi Neil,

      Portable jump starters are designed to output maximum current for a very short time… just long enough to start a vehicle. The current drops off very quickly after the initial burst of power. If you’re trying to start a car, the jump starter internal battery needs time between starts to recover.

      I love your idea, but you would only get power for a short time (10 or 20 seconds at most) before the jump starter shut down to protect its internal battery.

      The other option could be to get one of those huge jump starter packs designed to start large truck diesel engines. But that would be way more expensive than a dedicated battery and possibly heavier. I’m guessing weight’s an issue on your boat, so it’s probably not an option.

      Here’s a thought…

      Depending on your budget, I’d probably choose a Lithium battery like this one instead. It’s only 8kg and has a maximum continuous discharge of 85A for 40 minutes. You could take it home and charge it afterwards.

      Hope this helps.

      Cheers, Andrew


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