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Jump Starting 101


As we move into December, for most of us, that means we are dealing with much colder temperatures than we saw in recent weeks. Which brings all kinds of changes and adjustments to our routines. One big thing to contend with when temperatures drop is how it impacts your vehicle. A key aspect of this is your power system, specifically the impact of cold temperatures on your vehicle’s battery(ies). This issue isn’t confined to traditional internal combustion engine (ICE) vehicles, as cold can cause problems for hybrid (HEV), plug-in hybrid (PHEV) and battery electric (BEV) vehicles as well. As we pointed out in a previous article, these non-ICE vehicles contain low voltage batteries that perform a variety of tasks, depending on which vehicle architecture they are deployed in. So, we thought we’d focus this month’s article on what to do when you encounter a depleted battery and need to perform a jump start. This is primarily related to ICE, HEV and PHEV vehicle types, but we’ll touch on BEV vehicles briefly as well.

Successful Jump Starting Starts with a Ready Unit

In life, where you end up often is a result of where you start. This is definitely true when it comes to jump starting. First, it is important to have a quality unit, that the unit is in proper working condition and that the unit is at or near full charge.

Let’s start with the charge. It doesn’t do you any good to have a jump starter, but when the moment comes when you need it, your jump starter is as deleted (or more depleted) than your disabled vehicle’s battery.  That’s why we recommend charging your jump starter (no matter the type) every 90 days. It is a great habit to get into, like changing your furnace filter – just do it.

Next is making sure that your jump starter is properly matched to the types of vehicles you plan to use it on. For most people, this is pretty straightforward. Most cars/SUVs/minivans have approximately the same starting need and, as such, all require about the same size jump starter. But, as we note above, weather has a hand in defining your starting need as well. So, if you live in a place that can get extremely cold, your chosen jump starter needs to have greater starting power than someone who lives, say, in Florida. If your application need is more diverse, this should be taken into account. For instance, if your pickup has two batteries, you own a high compression sports car or have a boat with a diesel engine, these starting tasks place more demand on a jump starter than standard passenger vehicles. Your jump starter decision should be driven by your most demanding starting task, which by default, means that it would be more than sufficient to start everything else in your garage/fleet.

Once you have a properly sized unit for your starting tasks and it is fully charged, the last prep step is to perform a visual inspection of the unit to ensure that it is in good condition and safe for use. This part of step 1 usually takes less than 10 seconds and is worth its weight. When we’re talking jump starting, safety should always come first and safety starts with ensuring your unit is in proper condition.

Here’s a quick checklist for your visual review:

  1. If your unit has a master ON/OFF switch, check to make sure that the ON/OFF switch is in the OFF position.
  2. Check that the clamps and cables are in good working order. Signs that the cables or clamps may be damaged include, but are not limited to the following:
    • Burn Marks on the Jaws
    • Damaged clamp handles
    • Damaged clamp springs
    • Damaged cables where copper wiring may be exposed (insulation jacket deteriorated, cut or missing).
  3. Check to make sure the case is not swollen, a sign of damaged battery(ies).
  4. Make sure that the unit is not connected to an AC outlet. The unit should never be connected to AC when performing a jump start routine or providing DC power to an accessory.

Verifying these simple check points before every use will keep your jump starter safe to use and increase its service life

Prepping Your Vehicle

Before you move to this step, remember your safety precautions when working around a battery. Wear eye protection, appropriate gloves for battery work, remove all jewelry and never smoke around batteries.

This step is also pretty simple. First, visually inspect your battery. Is there a bunch of corrosion on the terminals? If so, carefully clean the corrosion using warm water and baking soda, taking care not to expose sensitive electronics to water exposure. Then, wipe the battery down, since surface moisture on the top of a battery could cause a micro-short, which would sap the battery of its energy capacity. Make sure that all battery connections are secure and tight. Poor connections diminish the amount of energy that can reach the starter.

Confirm vehicle voltage. Again, this is really easy when you are only dealing with passenger vehicles, which are typically all 12 Volt. But, once we get into medium duty trucks, heavy duty trucks, implements and industrial equipment, it is critical to confirm voltage and ensure that your jump starter is properly matched to the required system voltage. Also, now is a great time to determine if your vehicle has alternate vehicle starting points, away from the battery – check the owner’s manual for the proper jump starting procedure for your specific vehicle(s). If your vehicle doesn’t feature alternate starting points, find a good vehicle ground for the negative jump starter connection, as we will note in the jump starting procedure.

Editor’s Note: We hear from many technicians and vehicle owners who note that they have performed dozens, even hundreds, of jump starts successfully and without incident while connecting the negative jump starter lead to the battery’s negative terminal. We get it – you’ve done it this way and had no issues. But, you shouldn’t. Full stop.

Lead acid batteries emit explosive gasses during normal operation, including when you were just cranking on it to get your vehicle to start (unsuccessfully). You never want to complete the circuit at the negative battery terminal, because you could create a spark, which could ignite those explosive gasses. We (and UL and every other safety/testing agency) want you to be safe every time you use our products. The safest, and only appropriate, way to make the connection for your negative jump starter lead is to clamp the negative (black, –) clamp to a vehicle ground (non-moving metal part). Do not connect to carburetor, fuel lines, or sheet metal body parts. Connect to a heavy gauge metal part of the frame or engine block.

Now we’re ready to perform the jump start.

Make it Happen

Now, with all the preliminaries out of the way, let’s get to the main event.

1 –  Use in a well ventilated area.

2 – Shield eyes. Always wear protective eyewear when working near batteries.

3 – Review this instruction manual and the instruction/safety manual provided by the manufacturer of the vehicle/equipment being jump started.

4 – Confirm vehicle voltage and that your jump starting equipment is capable of providing that voltage.

5 – Turn vehicle ignition off and ensure jump starter’s ON/OFF switch (if so equipped) is in the OFF position before making cable connections.

6 – Clamp the positive (red, +) clamp to the positive terminal on the vehicle battery (for negative ground system), or an alternate vehicle starting point as recommended by vehicle manufacturer.

7 – Clamp the negative (black, –) clamp to a vehicle engine or frame ground (non-moving metal part).

Note: Do not connect to carburetor, fuel lines, or sheet metal body parts. Connect to a heavy gauge metal part of the frame or engine block.

WARNING: If your unit is equipped with a warning buzzer and it beeps, do not advance to step 8. The warning buzzer indicates an unsafe starting condition, such as reverse polarity or mismatched voltage. Disconnect the negative clamp immediately. If you have an AGM battery equipped jump starter and it was exposed to an unsafe condition, remain away from the vehicle and unit for a minimum of 30 minutes to allow any flammable gasses to dissipate. Then, follow the lockout / tagout procedure below.

8 – Make sure the jump starter cables are not in the path of moving engine parts (belts, fans, etc.).

9 – Turn the jump starter’s ON/OFF switch, if so equipped, to the ON position.

10 – Stay clear of batteries while jump starting.

11 – Start the vehicle (turn on the vehicle ignition).

Note: if the vehicle doesn’t start within 6 seconds, let the jump starter cool for 3 minutes before attempting to start the vehicle again or you may damage the engine starter.

12 – When the vehicle is started, being careful of moving parts, disconnect the negative (-) battery clamp from the vehicle ground.

13 – Turn unit ON/OFF switch to OFF position.

14 – Disconnect the positive (+) clamp.

15 – Properly wrap cables and store clamps as intended, based on the jump starter’s design.

Lockout/Tagout of Mismatched Voltage Unit
Once a unit (and its batteries) has been exposed to a severe over-voltage condition, as outlined above, the safety mechanisms within the batteries’ construction are likely compromised. From that point forward, the batteries risk excessive gassing during normal use and must be replaced. A unit exposed to mismatched voltage (12V unit/24V system) should be immediately locked out of operation and tagged as unsafe for use. Batteries contained in such units should be replaced prior to further use.

What about BEVs – You said that they could be "Jump Started" also?

Virtually every EV model in North America features a 12 Volt (low voltage) battery as a critical component in its electrical system. Although this may seem anachronistic, once you break it down, it makes a lot of sense. In an article we reference in the above linked story, they quote a Hyundai engineer, who stated, “All the ECUs in the [BEV] are powered from the low voltage [battery], as well as the power relays that separate power from the high-voltage battery pack and the rest of the high-voltage network in the car. That separation allows us to safely disconnect the high voltage from the low voltage when the vehicle is not being driven or in the event of a crash.”

The moral of the story is the same for all BEVs. If the low voltage battery dies, the vehicle is essentially bricked. The good news is that the low voltage battery in a BEV can be “jump started.” The reason we put that term in quotes is that a BEV jump start isn’t really the same as an ICE vehicle jump start. In the case of an ICE vehicle jump start, we are providing a quick, high burst of power to turn the starter. In the case of the BEV “jump start,” we are providing augmented battery capacity to the low voltage battery so that it can perform its task. So, it’s more along the lines of providing a power supply to the BEV. The end result is the same – the vehicle can be started. And the good news is that the same jump starter can be used for both tasks (starting ICE vehicles and providing power supply to BEVs).

The specific jump starting procedure and location of the starting points will vary by BEV model. It makes a lot of sense to familiarize yourself with these two factors prior to the moment when you will need this information. For instance, most Tesla models feature starting points behind the front fascia, at the top of the front bumper. Knowing how to access those starting points before you ever need to can save a lot of anguish if you ever run into issues.

When the Dust Settles

Ok. You have successfully overcome your crisis moment, with the help of a quality, properly charged jump starter. Is that the end of the story? It shouldn’t be. Just as the start of the process involved both the jump starter and the vehicle, the end of the process should also.

In regards to the jump starter, if it came into contact with battery corrosion or other corrosive vehicle fluids, it is a good idea to wipe down the clamps and ensure the rest of the unit, such as the base, is clean and unsullied. This will help improve unit longevity and reliability. In addition, give the jump starter a charge, so it is ready the next time you call upon it. In regards to your vehicle, now’s the time to ask why the battery was low/depleted in the first place? Did someone leave a light on? No biggie and no further investigation is warranted. Does your vehicle suffer from excessive parasitic drain? It’s probably worth the effort to get to the bottom of it and get it resolved. Is your battery and the end of its useful life? Maybe it’s time to budget for a new battery. If so, keeping your jump starter fully charged is critical, since you’re likely to need it again until you get that new battery installed.

We hope this was helpful to you and addressed any uncertainty or unanswered questions you may have had. All vehicles are different, as are all jump starters, so you may have to adjust some steps slightly, based on your specific situation. Did we miss any questions you’d like to see answered? Please drop a note in the comments below.

15 Responses

  1. I have four batteries hooked up to a Pro Logix battery tender that I leave hooked up during our Michigan winter. It’s located in my pole barn, as I didn’t want to charge them inside my house. Is it ok to leave them hooked up thru the winter in my barn?

    1. Rich – Thanks for your question. Yes, it should be fine. Our PRO-LOGIX products are rated to approx. -30˚C (-23˚F). Lower than that could be a problem, but down to that point, you should be fine. Please remember never to attempt to charge a frozen battery. Thanks, Jim from Clore Automotive

  2. I have a 2015 Ford F-350 diesel; it has a two 12 volts battery system, one battery on each side of the engine compartment. I assume the batteries are arranged in a parallel configuration. At some point, I will probably need to use my JNC770 Jump-N-Carry to myself started. What is the correct way to jump start a two battery system?

    1. Paul – Thanks for your question. All of my research in the Ford Truck and diesel forums seem to indicate that you should connect to either of the batteries as you would if it were a single battery system (positive to battery positive, negative to a good engine or frame groun), since, as you note, the batteries are in parallel and are, essentially, as single combined entity. That said, one is going to be closer to the starter than the other, so if it were me, that’s the one I would connect my jump starter to. If any other subscribers would like to add thoughts or tips, I am sure Paul would appreciate it. Thanks, Jim from Clore Automotive

  3. Always the best information from the source of the power supply(CORE) Thank you.

    I just need to lock in my mind + first and – second when connecting
    – first and + second when disconnecting

  4. Is it safe to keep the charger plugged into the wall socket in the garage overnight, or should I keep “routine” 6 month recharges using fewer hours (for example, 6 vs. 12 hours?).

    1. Jay – Thanks for your question. If your unit is a Jump-N-Carry or Booster PAC unit, it is safe to keep plugged in to AC without adverse consequences. If your choose not to do so, we recommend charging every 90 days. Thanks, Jim from Clore Automotive

  5. I have a Pro-Logix 12 volt Intelligent Maintenance Station that’s hooked up to 4 batteries in my unheated barn. Is it ok to charge batteries with this charger in cold temperatures ?

    1. Richard – Thanks for your question. Yes, it should be fine. Our PRO-LOGIX products are rated to approx. -30˚C (-23˚F). Lower than that could be a problem, but down to that point, you should be fine. Please remember never to attempt to charge a frozen battery. Thanks, Jim from Clore Automotive

    1. Dennis – Depressing the red button will activate the gauge, so that you can check the vbattery’s state of charger (SoC). Thanks, Jim from Clore Automotive

  6. I have an AC plug in my 2024 Alfa Romeo which is activated when the vehicle is started or just turned on.Can I keep the JNC 660 left plugged in or will it hurt the 660.

    1. John – Thanks for your question. As long as you are charging through the built-in 120VAC charger (two tines sticking out the unit) using an extansion cord, that method is automatic and cannot result in an overcharge. You will be good. Conversely, using the male-male DC extension cord to connect to a vehicle 12V power port must be monitored, as it can result in overcharge. Thanks, Jim from Clore Automotive

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