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A few years ago, I ordered a replacement cell phone battery from Amazon, and while it worked, it didn't last as long as I expected. I wondered if the seller had scammed me by selling me a battery that had been previously used, so it gone through a few dozen (or hundred) discharge cycles and had a lower capacity than a new battery would have. That phone is long-dead by now, but I still wonder: was there some way I could have tested the battery when I received it, to tell if I had truly gotten a new, never-been-used battery as advertised?

In my attempts to search the previous questions here, I've found several references to internal resistance increasing as a lithium-ion battery pack ages, so that's a partial answer to my question. But I still have two things I haven't been able to find answers to yet:

1) Would all lithium-ion battery packs have the same low internal resistance if they are new? (Or at least, all battery packs intended for use in smartphones, which means their physical size and voltage will be roughly similar to each other even though there will be some variance.) Or do different lithium-ion batteries vary too widely for this question to be answerable without a model number? (In which case I would have to find the manufacturer's data sheet for that battery to know what its internal resistance should be when new.)

2) Can I measure that internal resistance with a multimeter, and if so, how? Can I simply set the multimeter to resistance mode, then touch the red probe to the battery's positive terminal and the black probe to the negative terminal? And a sub-question: is this safe? As I understand multimeters, when in resistance mode they put a small voltage across the probes, so that a trickle current would pass through the battery. I don't think that this would be dangerous to the battery, but I'm certainly no expert. (I understand enough about electronics to know that V=IR, and to know how to use a multimeter, but that approaches the limit of my knowledge. I'm a software developer, not a electronics engineer.) So if this is dangerous and I shouldn't do it, I'd rather find out now than by having a battery explode in my face. :-)

NOTE: The question I'm asking is close to How to measure capacity of a Lithium-ion battery, but I'm coming at it from a slightly different approach. I want to know whether I can tell if the battery is new if it's been heavily used (where "heavily" is a little vague, but I'd define it as "enough to make a significant, measurable difference when compared to a brand-new battery of the same type"). Maybe measuring the capacity is exactly what I need, but I'm too ignorant to know how to interpret the capacity results to tell if the battery is new. If that's the case, please feel free to close this question as a dupe, but I'd appreciate a brief explanation of how I should interpret the capacity results. :-)

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    \$\begingroup\$ To use a DMM to answer your question , no. You cannot tell the age remaining if a battery or even the dynamic aging rate. This has a strong temperature and DoD dependency. You would have to know the C ratio max for the battery specs to know if your application exceeded the specs. Then you would have to know what specs apply to this pack and how to verify them at different rates. Typically what happens with cheap quality sources if lack of specs and high ESR effects that accelerate aging rate rapidly. Pulsed Isc with a current sense R for 10A or more at be the acid test. \$\endgroup\$ – Sunnyskyguy EE75 Jul 12 '18 at 3:54
  • \$\begingroup\$ @TonyEErocketscientist - I could figure out that DoD is "depth of discharge" with a quick Google search, but I've been unable to figure out what the C ratio is. I found a term called C-rate, but not C ratio. Is C ratio something else, or did you mean C rate? \$\endgroup\$ – rmunn Jul 12 '18 at 3:58
  • \$\begingroup\$ Yes C rate is a ratio to the 1h capacity \$\endgroup\$ – Sunnyskyguy EE75 Jul 12 '18 at 3:59
  • \$\begingroup\$ lipolbattery.com/… \$\endgroup\$ – Sunnyskyguy EE75 Jul 12 '18 at 4:02
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Whether a battery is brand new should be detectable from quality of housing and printed datacode. However, determining if a battery is "brand new" in not a very useful parameter. Manufacturers of smartphones/tablets can use different sources for Li-Ion batteries, and after-market batteries may have a different (even a bigger) "rated" capacity than the original battery. However, actual capacity of Li-Ion batteries varies depending on charge-discharge rate, and battery temperature. So the results of measurements might disappoint.

Regarding the question (1), no, according to Battery University article, BU-902: How to Measure Internal Resistance, the DC battery impedance is not a very good indicator of battery SOH - State of Health. The impedance would go down significantly when the battery is really EOL. Regarding how much the internal resistance varies from one battery of about same size, yes, it differs for "low discharge" batteries as compared to "high-discharge" batteries, this is one of design parameters.

The same article also explains how to measure internal resistance of a battery. Your idea of measuring it with DMM in Ohmmeter mode is absolutely wrong. The article also explains that the battery equivalent model has more than one impedance, depending of load frequency you will get different results. The simplest approach is to measure the lump DC impedance, but it is a poor indicator of battery health.

Finally, no, you can't tell if the battery is good with simple DMM measurement. The only right approach is to measure the actual battery capacity under conditions specified by manufacturer, using approaches as explained in the linked SE answer. And then compare the result with either advertised capacity, or to batteries with similar size and construction. A load of information about actual performance of batteries can be found on this website, lygte-info.com

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  • \$\begingroup\$ Date code is useless. Besides sitting in storage for a while I can transform a lipo battery from "brand spanking new" to " dangerous pile of toxic waste" in well under a day \$\endgroup\$ – PlasmaHH Jul 12 '18 at 6:54

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