Thursday, July 16, 2020

Can't Live With 'Em ...

You know the rest.  In this case, the 'them' is batteries.  Can't live with 'em, can't live without 'em.

Like a lot of you, I've had a jump starter battery that I keep in the car for emergencies for a while; I got my first one back in '14.  That first one died pretty quickly as a result of being left in the car during the day while at work.  It's replacement was upgraded a bit; that first one was an 11 Amp*Hour (AH) battery, and got replaced by a 15 AH.  The other day, I realized I hadn't run a battery analyzer discharge/charge cycle on that replacement battery for quite a while.   

This isn't really the story for tonight, but I tested that battery a few times.  I tested at the 5 hour discharge rate (C/5, or 3A) and at the 10 hour discharge rate (C/10 or 1.5A).  Neither test came close to the rated 15 AH capacity.  The measured data was close to 25% of rated - 3.5 to 3.7 AH.  It stayed that way after four cycles of discharge/recharge but then I dropped it and the plastic case broke in two.  That revealed the battery, a lithium battery, had swollen and I couldn't get the case back on.

So it was time to order an replacement, and I found an unknown brand replacement on sale (the one I had was unknown when I bought it, too).  It was rated 18 AH, so another upgrade; this was 20% bigger than the broken one and 64% bigger than the first one.  It's rated 800 cranking amps, for "up to 7.0L Gas" engines, much larger than either of my cars.  Plus it has the same output marked 12V 10A the previous one had, and that I plan as an emergency, last resort, backup power for ham radio.  I use this port to test the battery, too. 

When it came in last Sunday, of course, I topped off the battery on the charger and reran the test.  The capacity came out almost identical to my previous battery.  Here's the data:

It was clearly time to ask myself if I knew what I was doing.  Time to sit down with the manual (well, brochure).

In the specs, it says it's an 18,000 milliamp hour battery, so I just call that 18 Amp Hour.  For most rechargeable batteries, from Nickle Hydride AAs to AGM lead acid, the test I was doing was proper.  I discharged it at the C/10 rate, 1.8 Amps, and it came up at about 3.6AH to the (approx) 33% charged level.  Looking a little closer in the manual it says 66.6 Watt Hours.  It's not exactly 12V to start and the voltage slowly goes down over the discharge.  If I take the middle voltage (11.125V) and multiply by the 3.6 AH of discharge, that works out to about 40 Watt Hours, rather close to 60 % of the 66.6AH rating.  The numbers are starting to make sense. 

If it was really a constant 12V, 66.6 Watt hours would work out to be about 5.6 Amp Hours capacity which is a far, far cry from 18AH.  I see two possibilities: either it's just a sales claim and they're trying to sound good (this used to be legendary with stereo systems back in the day), or the battery is internally different and actually is designed differently for "cold cranking amps" like any other starting battery, not for a steady 10 hour discharge.  I'm leaning toward the second choice; that it's a starting battery designed for enormous loads on rare occasions and then it gets recharged.  I don't know enough about lithium batteries to know how they'd do that, but I barely understand the difference when making a lead-acid battery; in those it's the way the plates are made. 

It seems the best way to test it as a starting battery is something that can measure cranking amps.  Since it's not specified for slow discharges, I'm afraid I'm stuck with an "it is what it is."  I'll just run the discharge tests every six months or so and keep track of how it changes vs. time. 

I'm posting this for you, of course.  The 66.6 Watt Hour spec doesn't appear anywhere on that Amazon product page that I can find.  It's in the fine print in the paper manual that came with the battery.  That seems to be the most honest rating of the battery. 


  1. Do you use this for emergency starting? If it’s for ‘other’ uses, ok, but there are miracle car starters out there now; a complete bafflement to this old guy.
    My son gave me a gizmo that will start my old 350 v8 dump truck, as well as my diesel tractor (used on both). Check ‘em out... mine is this one:
    Then, you can recharge the unit from the now running vehicle.
    Amazing gadgets that work!

    1. The coincidence is that is the update to the one I dropped and broke. I know GooLoo, and actually jump started my car when the alternator died a few months ago.

      The one I had is obsolete now, but same basic package, five blue LEDs and everything, except it was rated 15 AH instead of 18.

  2. When I got a trailer and started into RVing, I came across this book: RV Electrical Systems by Bill Moeller. I learned more about 12v systems from him than my previous fifty years experience with auto mechanics, not least of which is theory and practice of multi-stage charging.
    I was reading it on one of our first winter camping trips, and my wife was watching one of the early episodes of Breaking Bad, where Walt and Jesse are stranded with the RV's house and starting batteries dead. They pull out a generator to recharge and it catches fire. I told her that was EXACTLY why I was reading that book!

  3. You have what's called a "3S" pack in the R/C world, something I've learned a LOT about in the last year since I picked up the R/C hobby again.

    The cells are made by the zillion, poorly graded, slapped into packs, and sold cheap because they are cheap. The come in a wide range of sizes and ratings, and the guys who are seriously into R/C have made an extremely thorough study of them.

    Your measurement technique is acceptable. There's no "magic" about a LiPo, and if it's rated 10Ahr, it should be able to meet that spec.

    90% of them fail miserably at meeting their published specs. Some of it definitely reminds me of the "Output Power Wars" stereo equipment went through, but a large part is just fraud. They KNOW nobody's going to test them but a few geeks like us, so....they lie.

    What size wire leads are on the pack? What connectors are they using? Unless they're 8/10ga, there's no way you can pull "800 Cold Cranking Amps" out of it.

    I've had numerous friends who got burned on those little jump-starters, although some of the newer ones with LiPo's are supposed to be quite good.

    1. Thanks DrJim, that's the best summary of read of these things anywhere!

      The cables are marked 8 AWG, but the copper isn't actually visible. The cable could be molded cheese for all I know. It uses a large connector, like my others have, which means it's not that out of line with others. When my alternator died back last winter, I used the predecessor charger several times, but my engine is 4 Liter V6 and I'm sure it doesn't take 800 CCA.

      While searching the Amazon page, I ran into something that's a red flag "if I knew then what I know now". It says the pack can be recharged from dead to full in 4.5 hours. Now that I have one I know the charger is a 15V, 1A wall wart. Now how does 4.5 hours delivering 1 amp turn into 18 AH? Even if you give every possible benefit of doubt, and say that's 15 Watts, in 4.5 hours you have 67.5 WH, which is the closest to the spec of 66.6 that I've seen.

    2. The marketing math here is straightforward and deceptive. Agree with your hunch that the manual's 66.6 Wh rating is truthful. We might equivalently describe the battery pack as 6 Ah at 11.1 V. Note 6 Ah times 11.1 V equals 66.6 Wh.

      Next, drjim has postulated the battery pack is composed of lithium polymer cells in a 3S configuration. I agree. Three cells in series. LiPo cells generally are described as having nominal voltage of 3.7 V each. 3 times 3.7 V equals 11.1 V.

      Next recall the capacity of the battery pack is 6 Ah. Cells of the pack are connected in series. So each of the three cells could be labeled as 6 Ah, assuming 3.7 V per cell.

      Methinks some marketing dumbass unfamiliar with series and parallel arithmetic saw three cells inside the battery pack, each labeled as 6 Ah. Said dumbass computed 6 times 3 equals 18 and plastered an "18 Ah" rating on the package. Discrepancy solved.

      I thought you were some sort of radio engineer?

    3. Yes, when I first put it on the battery analyzer, it "suggests" the battery is 11.1V and three cells. Whether the reason for calling it 18AH is as you suggest is speculative, but all I know is what I measure and it's certainly not 18 AH. It might well be 6AH.

      I thought you were some sort of radio engineer? I got a laugh out of this. The sort of radio engineer I am now is "retired." Before that, the sort was "career long". Radio Frequency engineer does not overlap with battery engineer. I worked on exactly one radio that was to be battery powered, back around 1990. The company I call Major Southeast Defense Contractor had a power supply engineer design that.

      All I know about lithium batteries has been hobby-associated reading and experimenting.

  4. If I could just remember to turn my headlamps off....

  5. Does 18 AH @ 3.7 Volts seem about right?

    1. I'm not 100% sure I get the question, but if you're asking if it's reasonable I have three 3.7V 18 AH batteries in series to make the 11.1V output, no. That's not what I measure.

      When batteries are added in series, the current doesn't add, just the voltage. I cut the test at about 3.6 AH when it seemed close to the rapid voltage drop at the end of capacity. What I seem to have is three 3.7V 3.5 to 4 AH batteries in series.

      To add currents, the batteries would have to be in parallel connections of three battery series strings. For the sake of illustration, if the batteries were 3.6 AH (just a bit less than I measured), there would need to be five parallel strings of three batteries in series. 15 cells. But if that was what was inside the box, I would have measured close to 18 AH, not 3.6.

  6. You got what was specified...

    The CELL is 18AH but the votlages is 3.7V nominal or about 66WH.
    I hear everyone going wut? Its not a 12V battery in there its a single LiPo or LiFepo and a pover converter to deliver a peak current for maybe 10 seconds of maybe 800A. Use Watts/time and 66Wh for one minute can easily be 3900watt/minute. Ohms law and resistance will limit that greatly.

    So your testing says 66wh for 5 hour rate is likely correct.

    FYI for those that insist it was a 3S pack of 1AH cells if it were
    then that would be a 205WH battery or 18AH times 11.4V nominal.


    1. I doesn't look like that's how it could be.

      That plot in the post shows what looks to be an unregulated output that's labeled 12V 10A. It's pretty much the same as what 3 unregulated Li-Ion cells in series would do. If it's a single 3.7V cell with a power circuit, that's one strange little voltage regulator.

      There are other outputs on the box, both USB format. USB regulators are cheap, and I expect them to be better regulated than the 12V output.

      If the listing had said that everything is limited to 66.6 AH, I'm not sure I would have bought it.