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. :-)