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Q&A Related to Jump Starter Health



We get a lot of phone calls, email inquiries, Facebook posts and blog comments related to jump starter health. After “Where can I go to buy your products?,” it is probably the question most frequently asked of us. Sometimes, the question is very specific, relating to a jump starting situation or use case that makes it quite unique. Most of the time, though, these questions fall within several common areas of concern. So, we thought we’d address them in a blog post in the hopes that we can help dispel any misbegotten notions and arm you with the information you need to get the most out of your jump starter investment.

How often should I charge my unit?

This one comes up a lot. If you are a high volume user, you have likely found your rhythm, but we’ll address those use cases as well as less frequent use case. We’d love you to charge the unit after each use, but we know that may not be realistic in all situations. So, if you are running a mobile service operation or other non-stationary function, we strongly suggest charging overnight whenever the unit has been used to jump or serve as a power supply. Putting the unit on a charger at 7 p.m. should bring it to full charge before the next work day begins. For occasional users, we suggest charging after each use and every 90 days when the unit has not been used. Keeping your unit at or near full charge is the number one predictor of unit longevity, so give it a charge.

Note: We offer recharge alerts to help you to remember to recharge every 90 days. If you haven’t done so already, you can sign up for these by clicking here.

I received my recharge alert and went to charge my unit, but the light was green. Does that mean I shouldn’t charge it?

No. We still suggest charging the unit for 4-6 hours. Although the charger may not turn on if the unit is fully charged, if it is slightly below full charge yet high enough to trigger the green light, doing so will bring the unit back to a full, beneficial charge.

Similar, but different than the above. When I purchased my jump starter, the manual and carton said to charge it for 24 hours upon initial purchase, but when I went to do so, the light was green.

First, this confuses a lot of people. It is important to understand that some units go from manufacturing to the final user very quickly and others move more slowly. So, we ask all purchasers to charge their unit upon purchase, since we can’t be sure which ones really require the charge. But, like the above answer, we encourage all purchasers, even those that get a green light to charge for 4-6 hours upon purchase.

Is it OK to leave the unit connected to AC power continuously?

For current generation units, the answer is yes, absolutely. For older units, the answers is more, “it depends.” For Booster PAC and Truck PAC models, yes you can do this regardless of vintage. Same is true for all vintages of JNC770, JNCAIR, JNC950 and JNC1224 models. For JNC4000 and JNC660 models, if you have LEDs showing CHARGING and CHARGED on the face, you can remain connected to AC indefinitely. For JNC300XL models, if you have a BC icon on the bottom label, you can as well. Otherwise, charge overnight and then remove the unit from the charger.

Can I leave my jump starter in the car during the winter? After all, the manual states that the ideal storage temperature is 70˚F.

The easy answer is yes. Like your vehicle battery, the unit should perform well until it encounters extreme temperatures. Our general rule of thumb is if the unit is going to see temperatures below -20˚F, you might want to consider bringing it in overnight. Also, during extended extreme cold stretches, we recommend charging every 30 days vs the normal 90 day charging interval. When bringing the unit in to charge in extreme temps, allow it to warm up for 30 minutes or so prior to charging. The battery will take the charge more readily if you do so.

What if I haven’t used or charged the unit for 2 years? Why isn’t it working?

Like your vehicle battery, if a jump starter is allowed to sit for a very long time without activity, its battery’s internal chemistry will begin to deteriorate. Eventually, its ability to accept a charge is compromised and the battery is rendered useless. Just as you’d never expect to start a vehicle that sat in the driveway for 2 years without replacing the battery first, the same is true for a jump starter.

What about lithium units? I have read that they can go a year without needing a charge?

Lithium jump starters are not too different from the other lithium battery driven devices in your life, whether it be a phone, tablet or other item. You wouldn’t expect to be able to put your phone in a drawer for a year and come back and use it as if you last touched it yesterday. Same is true for lithium jump starters. Like our lead acid units, we recommend charging them every 90 days when not in use, daily if used regularly.

My jump starter included a DC charging cord. Should I use that or the AC charging method?

The DC charging method, using the supplied cord, should be used only in those times when the AC charging method isn’t viable. For example, you do not have access to an AC outlet, but need to recharge the unit. In those times where it is necessary to use the DC method, there are a few things to remember. The first is that the DC power port on your jump starter is a direct feed to the internal battery, so care must be taken not to overcharge the jump starter. Frequently monitor the voltmeter and watch its progress. Once your reach 13.0-13.2VDC state of charge, you should disconnect. Second, it is important to remember that the output of your vehicle’s power port is quite high in comparison to the output of your AC charging system. That means that the unit could be recharged very quickly using the DC charging method. So, please don’t connect in this fashion and check back an hour later. It might be too late.

I think I lost my wall charger. I found one that fits, can I use it?

No matter the type of jump starter you own (lead acid, lithium, ultracapacitor, other), it is really important to use only the wall charger specifically designed to match the needs of your unit. Each wall charger model could potentially output a different voltage and amperage. All batteries are sensitive to overvoltage conditions and they should be avoided at all times. When in doubt, check with us. We’ll confirm that you have the right one, or we’ll help you get what you need.

We hope you find this helpful. Our jump starters typically last a good length of time, but remembering the above answers/tips will help you get the maximum life from your unit. And remember to sign up for recharge alerts if you haven’t done so already.

16 Responses

  1. Good night! I have a Shumacher she jump starter. It’s brand new, never been used or charged sitting in storage for about 2yrs. I put it to charge for like 72 hrs and the compressor works but when I turn on the jumper the battery indicator is red. Any info woul be appreciated.

    1. Anthony – Thanks for your comment. If it were our unit, we would ask if it was regularly charged during the 2 years of storage? If not, the battery is likely compromised. This would explain why the battery indicator is red. Like your car battery, without regular charging, the health of your jump starter battery will degrade over time. Thanks, Jim from Clore Automotive

  2. I purchased a brand new jnc660. Charged it completely. After 2 weeks of sitting volt meter shows 12.8 volts. Is this normal?
    I plugged it back into ac light shows Charging?
    Thank You

    1. Russ – Thanks for your question. 12.8V is fully charged for a 12V AGM battery. It will not hurt to plug it in and charge, but the charger will turn off quite quickly and go to charge complete. But, your unit is fully charged when it is at 12.8V. Thanks, Jim from Clore Automotive

  3. I’ve a Schumacher jump starter for a while. I didn’t know I had to charge it immediately after getting it so I have never charged it. Just to see, I pressed the battery status button and it lit up the mid-level charge indicator. Do I need to replace it or can I just charge it up and keep it charged from now on?

    1. Aerika – Thanks for your question. As you know, we do not manufacture Schumacher products, but yes, jump starters must be charged periodically. We recommend charging every 90 days. Whether or not the unit can be salvaged depends on how long it has sat without changing. If it is over 18 months, it likely caannot be recovered. If less, there’s still a chance. I would suggest that you charge the unit for 24 hours. Then, check the battery status (it should be full). Then, 3 days later, check it again. If totally dead, the unit likely is sulfated. If the unit shows any charge, repeat the process 2-3 more times. Hopefully, but the end, you will have recovered the battery. Thanks, Jim from Clore Automotive

  4. If there is no charge left in the portable unit after hours of trying to recharge is the entire unit worthless or can u purchase a battery for the charger!

    1. Anthony – We are sorry that you are have an issue. I suggest that you call our Tech line at [800] 328 2921, option 2. They should be able to help diagnose the issue. Thanks, Jim from CLore Automotive

      1. Jnc660 charger reads over 12, in the green. Green fully charged light does not come on. Yellow charging light sometimes solid, sometimes flashing. Unit charged every 3 months but not used. Bought for emergencies. Is this normal?

        1. Mark – Thanks for your question. Fully charged, the gauge should read 12.8-12.9V. If you are getting the unit to this area after an overnight charge, you should be fine. Sometimes, the battery could sit just below (0.1V) below the threshold for lighting the green light, but is still charging fine and giving the battery a full and complete charge. Thanks, Jim from Clore Automotive

  5. I’ve worked around Deep Cycle Batteries for a long time. Such as Golf Carts. I know that they have to have a trace charge to energize the charger. If the batteries are completely dead, you can trick the charger into working by using a remote charger directly connected to the batteries. Can you do this with a jumper box?

    1. Buddy – In theory, yes, that should work. That said, our jump starters are 12V and 24V, while most golf cart batteries are 36V or 48V, so probably would not be adequate for the task. We are very stringent about matching voltages, because mismatched voltages result in very unsafe conditions and dangerous outcomes. Thanks, Jim from Clore Automotive

  6. Hello. Forgive me if this has been covered. If it has I didn’t see it.
    Can I charge my JNC770 through the AC outlet on my truck? I do not want to compromise the charging system on my truck or the health of the JNC. I believe the AC outlet is 150 watts.
    Thanks. Rob

    1. Rob – Thanks for your question. Yes, this should be no issue. Use a standard extension cord to connect the JNC770 charger to your truck’s AC outlet. The JNC770 charger has a low draw and should not present an issue whatsoever to your truck, nor should it cause any problem with your jump starter. Thank you, Jim from Clore Automotive

  7. Hi,

    I see your lithium ion jumpers (except those costing around $1,000) and even some of your lead acid jumpers have quite low maximum states of charge, such as 84 watt hours for one of your Li ion units. My education and experience suggests that the JNC660 with 22 amp hours is a minimum (with amps=watts/volts, 22 amp hours = 264 amp hours @ 12 volts). This gives it 3.14X the wattage or amps of your Li unit. Further, wouldn’t you agree that CCA (cold cranking amps=the # of amps produced by a fully charged battery at 0 degrees F while maintaining at least 7.2 volts) should be a measure that you provide as well as CA and amp hours? Also, for comparison purposes wouldn’t it make sense to have the same measurements and same terminology (CCA, CA, Amp hours instead of Watt hours, etc.) ?

    Separately, why do you not include an AC power cord with your JNC660? My toaster came with its own power cord.


    1. John – Thanks for your comments/questions. Because the lithium units are much more energy dense, the amp hours (when using as a jump starter) are less relevant. That’s why they can having relatively low amps hours and start vehicles with ease. Unless you are using the units for power supply purposes, amp hours is an apples/oranges situation in terms of comparing the power of a lithium unit and lead acid unit. We choose not to provide CCA details for a wide range of reasons, number one being that vehicle batteries are sized based on the totality of their intended functions and are, therefore, their CCA output is not necessarily correlated to the specific starting need of the vehicle. So, CCA causes a lot of confusion. We have never included a power cord with the JNC660. It has always been built as a pro-first product and the typical shop has dozens of power cords. Including a power cord adds cost but brings very little value. Thanks, Jim from Clore Automotive

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