To point out something else here, there should be no electrical difference between hooking up another battery in parallel (like jump starting) and just straight replacing a battery. I always do it with both cars off initially and if I feel that a little more juice is needed I’ll start the donor car after everything is connected.
I think it is wise to buy the biggest capacity battery you can fit once the factory one dies. That way you can jump others if need be and the additional capacity means you can be in the “marginal” range longer and still be okay.
BoingBoing’s advertising policy used to claim that they would say explicitly when something is an advertisement or paid content.
In this case, Mark (a maker who knows his stuff) is endorsing a product he has never used. It’s one thing to show folks a cool product and talk about how neat it is (a Dr. Who box set for instance). When it’s a product designed to be used in an emergency, it would be nice to see a little higher bar for endorsement than “this thing exists and can be purchased.”
It’s energy rather than power. 600A of cranking draws the equivalent of nearly 8kW from the battery (allowing for internal resistance), which means that 10 seconds of cranking could be anything from 20 to 50 kJoules depending on temperature. A 2AH 15V lithium battery holds around 100kJ, so if you can use that energy efficiently (by charging a working lead acid battery) you could get several starts out of it.
Capacity is less important than maximum cranking amps (CCA, measured in A to the SAE standard) and the general robustness of the battery. In fact, a bigger capacity battery of the same dimensions and weight will need thinner plates, good for short circuit but bad for durability. Original manufacturers generally put in better batteries than the run of after market ones (because warranty claims are expensive). The “best” battery is likely to be the heaviest (most lead), with the highest SAE CCA (cranking) and the largest number of rated cycles to 50% discharge. Be dubious of batteries which only quote 25% discharge. But it may not have the highest capacity. A battery that can withstand 90 cycles to 50% capacity is less likely to let you down than one only quoted to 25%, and in reality has a higher working capacity than such a battery.
Wrong way round. The biggest risk of a voltage surge due to a momentary battery disconnect is at startup when the engine thrashes around. With the engine at tickover you know that everything is under control. And you can check the battery voltage before proceeding. What, you don’t carry a $25 multimeter in your car toolkit? You should.
If the negative lead is making a poor connection at the battery then connecting between frame ground and anode will result in the full alternator voltage - which may be much higher than the battery voltage - coming on the jump leads. If the recipient battery has a loss of short capability due to high internal resistance, the jump leads may apply excessive volts to the recipient car. Although the probability of this is not high you should always connect to the battery terminals directly. The risk of a hydrogen explosion due to outgassing is pretty low, as with the hood open hydrogen dissipates very rapidly; also there should be no air in the cells so the risk of cell detonation isn’t worth considering also if the cells are properly maintained there should be insufficient gas volume in the cells to cause cell detonation. I do know someone who managed to create a hydrogen explosion using lead acid batteries, but that was in a boat where the battery ventilation did not comply with standard - and you might be surprised just how small a ventilator is needed.
There is a potential problem in hot climates where under-hood temperatures may become very excessive. This can cause battery drying out and overheating. I’ve made this observation below but, although in the heat of the moment it may be difficult to remember, before jump starting the donor battery should always be checked for safe condition.
I haven’t used this exact device but I own a similar device by another company. I was gone for 16 days, when I got home my car wouldn’t start. Grabbed my gadget and gave it a try–it started right up.
I have jumper cables but since my wife doesn’t drive we have only one car–nothing to jump from.
I am not convinced. If a spark occurs at the final connection (which it has in at least half of the many, many jumpstarts I’ve performed), you do not want that happening right at the battery, where it says in not-very-fine print that you should keep sparks and open flame away. Certainly hydrogen gas will dissipate rapidly, but are you seriously suggesting it’s perfectly fine to cause a spark directly at the source of potential hydrogen off-gassing?
Also, in a hot climate like Southern California where I live, plenty of older batteries that might require a jump start have evaporated a certain amount of their electrolyte (which is why they need a jump start), and there may very well be air in the cells. I’ve certainly seen it, even on “maintenance-free” batteries.
Car batteries fail all the time… none of them lasts for more than a handful of years. Poor battery connections that might cause the short condition you describe generally take longer to develop, like after the first and even second batteries have been changed. I’m just one guy with my own store of anecdotal evidence, but I’ve never experienced a jump-start that damaged either car’s charging or electrical systems due to a voltage surge… but I have seen batteries explode due to connecting them the way you recommend.
true - supposedly you can jump a prius with a couple of lantern batteries, since all you’re trying to do is get the computer to boot so it can bring the HV battery online. never tried it on my prii though.
I have considerable experience with hydrogen. If you have managed to make a car battery explode by an electric spark near the vents, under normal operating conditions, I’m quite impressed. The 2008 paper HYDROGEN GAS MANAGEMENT FOR FLOODED LEAD ACID BATTERIES (Carey O’Donnell and Michael Schiemann Mesa Technical Associates, Inc./Hoppecke Batterien GmbH & Co KG) to which I just referred talks about the risk from outgassing in large lead acid systems, not small cells typical of cars. I referenced this paper when setting up a domestic lead acid system in a boat, in the engine compartment.
My short advice to anybody reading these posts is this: before using another car to jump-start, check:
The battery used to jump start is not hot, bulging or showing signs of distress
There are no signs of liquid around the vents
Ventilation is ample (i.e. hood is up and any cover over the battery has been removed.)
Then make your mind up where you are going to attach the negative cable. If you think ignition of hydrogen is a risk, connect to chassis. This does not constitute engineering advice (if it did you would be paying me for it and I would be covered by my liability insurance.) All jump starting has potential hazards and is at your own risk.
Not at all. I’m happy actual engineers are chiming in. And I’m not offended in the least.
I think my model is likely more finicky than others. As a distractable youth, I had to jump my Corolla way more than I should have, without incident.
My Lexus just sizzled on the second jump ever, doing it in the “proper” method. My mechanic (also a Lexus owner) insisted that it was the fact that I chose to jump it at all with another modern car.
The upshot is we just installed another dash, erasing 3000 miles from my odometer! Magic!
To each their own. I’ll agree that a running car is pretty much in a steady state condition, however the minute you drop a semi-shorted lead acid into the mix it’s going to be hard to tell what all the electronics are going to do. Having both batteries connected before cranking either vehicle does nothing more than present a now semi-degraded battery (one at say 90% capacity and one at 40%, so together enough to start either car). And no I don’t carry a multimeter in my car for the explicit purpose of testing the battery…most still show +12V even though the internal cell is starting to short and unless presented under load will appear fine.
