Jumpstart batteries and why mAh capacity is silly.

LittleDog

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With reference to another poster regarding jump start batteries and how they often do not provide a mAh rating for them.

Yeah, I saw that. I'm a numbers guy, and it makes me nervous when they don't post a simple number like XX,XXXmAh capacity.

I just used my Noco GB150 to jump a stranger's car in a parking lot yesterday and it handled it with no problem. I got the, "oh, all the attachments and junk inside that vehicle makes me think that person could probably help me get my car started" look again. I usually wait a while before cranking, but the largest Noco jumper has a voltage meter on it and the "dead" battery said 12.4V as soon as I plugged it in, so I had the guy crank it right away and it turned over without a struggle. In the past, I have used it to "trickle-charge" extra-dead batteries that wouldn't crank right away.

I, personally, have bought into this brand and have several of their products, but I don't think that they would be particularly much better or worse than any other established brand. If there had been something else on sale that first day, I might have too many batteries of another brand instead, because the specifics on the battery are somewhat vague.

The GB150 also doesn't give you a mAh number. When pretending to calculate running times for camping with peripherals and an Engel freezer, I was using 80 Wh, but I think it was 8,000mAh at 11-12V; you can probably find the exact quantity and precise capacity of the cells it uses in a tear-down video or something, but that total base number doesn't take everything into account.

Noco does try to sell you their most prominent number, in this case, 4000 amps for cranking. Cold cranking amps was pretty much all the information any jumper battery brand ever gave you in the past, before everyone learned how many mAhs their phone contained, and how many times they could charge it from a certain power pack. For the record, that 4000 amp number must mean peak amps, because 4000 Cold Cranking Amps would be crazy. 550CCA would be a good jumper battery, 1000CCA could start a big tractor, 4000 CCA would probably start a diesel submarine.

They also imply great capacity by rather disingenuously saying "up to 40" starts per charge, but that's most likely going to be for forty four-bangers that are each an amp short of cranking, on a summer's day. Unless you're in charge of a motor pool, you, and they, probably only care about having enough to start one dead car, one time. Fake trickle-charging a crazy Wrangler JL auxiliary battery is outside of their purview.

I don't know exactly why the jumper battery companies don't give out mAh numbers, but they are mostly useless when talking about cold cranking a vehicle anyway. You don't know how much loss their system has, or what kind of cables they are using. Potential battery capacity bears little resemblance to energy being delivered and received at +-X Amps and +-Y Volts. I mean, even before a reasonable ~30% loss, what the heck is 80 Wh at their maximum 4000 Amps? Like 14.4 Amp minutes? 240mAh? (Disclaimer, I made that math up, but it does give you about 15 seconds of crank time for each of your forty cars) Big numbers are great marketing though, so we'll probably see it in the future, possibly to record with our 56.6 megapixel cell phone cameras with 10.2" 16K screens.

I think that at the amps, voltages, ohms, and overall losses involved here, it would be a disservice to give the consumer a best-case scenario number to allow them to attempt to compare 20,000mAh portable lithium cell phone charging batteries to 8,000mAh jump start batteries to typical 70,000mAh lead-acid car batteries. Especially when you include the weird, arbitrary ratings many manufacturers provide. 135,000mAh(at 0.815V)!!!!!!

Having said all that, outside of the wacky shenanigans of the 3.6l battery system, I do trust the GB150, and consider it overkill for starting most any other car or truck, despite the lack of "real" numbers, and marketing spin. Smaller models of any brand are also perfectly acceptable for any normal vehicle, but figuring out that battery-starter circuit diagram of the 3.6l JL is up to each individual. If you hook a jumper battery directly to the starter battery, it'll probably start. If you perform crazy wiring, jumping, and shorting gymnastics with your fuse box beforehand and hook one up to the main battery, it'll probably start. If you do nothing but hook it up to the main battery and hope for the best, don't wait at all, or do wait, or forget to pray to the gods of electricity, then I dunno, maybe? Depends on what colour your jeep is. I think it works better on Mon-Wed-Fridays, and when Jupiter aligns with Mars.

At this point, I'm pretty sure that just carrying an extra starter battery and a wrench is the cheapest, simplest, and most sure-fire solution for self-rescue in the 3.6l. Or a set of jumper cables and a wink if you're in civilization. Works on me. Makes me extra glad though that I have the 2 litre turbo with E-torque, aside from the fact that I now carry three fire extinguishers for fear of that scary 40V lithium battery bursting into flame on a sunny day. I think those additional 28 volts are the extra-combustible kind.


I wonder if you can still jump start a JL using that old, giant green brick of D-cell batteries plugged into the cigarette lighter?


tl;dr

I jump-started a car with a big lithium battery. VROOooom. I don't know exactly how big the battery is, but it doesn't really matter, because numbers are lies. You should buy the brand that gives you the best, or the most decals. I might be bad at math. Sometimes lithium-ion batteries spontaneously catch fire. If you wink at me, I'll hit you with 4000 peak amps, but probably only 550 or so CCA.
 

Jebiruph

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@LittleDog , I like your post, but just wanted to point out that the main battery is the starter battery and according to the owner's manual, injury or death may result from jump starting the aux battery.
 
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LittleDog

LittleDog

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@LittleDog , I like your post, but just wanted to point out that the main battery is the starter battery and according to the owner's manual, injury or death may result from jump starting the aux battery.

Whoops, you're right of course. With slight sarcasm, but no ill will at all directed at you, I should always mention that any advice I, or the internet, may give may be hazardous to your health. I think most every jumper battery, jumper cable, battery tender, or just plain battery nowadays already has that disclaimer though.

Of course, in the future, every vehicle might also have an "Improper use of this equipment may result in injury or death" disclaimer/no-liability-release-clause that we will have to sign off on before starting the engine each time.


Disclaimer: Doing Anything to your Vehicle may be grounds for voiding your Warranty.
 

TimmH

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Sorry but when you said
"4000 CCA would probably start a diesel submarine."

I couldn't help but imagine an infomercial with a guy saying "We are going to star THIS diesel submarine, using this triple A battery."
 
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