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I'm seeing wildly varying capacities that are seemingly fake on 18650 cells, such as these "9,800 mAh" ones on eBay, but are ~$1 / cell.

However, 'genuine' cells from Panasonic and similar name brands seem to top out around 3,500 mAh or so, but cost more like $8 / cell.

How can I tell true capacity apart from the lies?

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    \$\begingroup\$ If it looks too good to be true, it's too good to be true! Don't buy eBay low cost electrolytic capacitors either. \$\endgroup\$ – Neil_UK Mar 1 '16 at 9:57
  • \$\begingroup\$ Sure, but the capacities will rise gradually; how do I know what 'too good' is referenced against? \$\endgroup\$ – Ehryk Mar 2 '16 at 4:51
  • \$\begingroup\$ I don't think there is anything reputable over 3.5Ah. If you need to discharge rapidly (e.g., 10A or more) you want to get cells specifically designed for rapid discharge. Those will have slightly lower capacity. I think 3Ah is the current max in rapid discharge. 2.5, 2 and even 1.5Ah cells are still out there and are available. Buy from a reputable vendor! \$\endgroup\$ – mkeith Aug 1 '17 at 5:48
  • \$\begingroup\$ 18650 battery tests 2011 2012 \$\endgroup\$ – Bruce Abbott Aug 1 '17 at 6:11
  • \$\begingroup\$ I came to this question from google looking for an actual answer to what are the valid capacity ranges for 18650 lithium ion cells \$\endgroup\$ – Arthur Ulfeldt Sep 24 at 17:43
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Obviously when you already have one in your hands, you can measure its true capacity.

However lets for a moment think about where these fake cells might come from:

  • Cheap companies that have little expertise in bleeding edge battery technology
  • Contracted factories that just leave the machines running for a while after they produce the parts for high end battery companies

In the first case you can be sure that the real capacity is on a much lower level.

In the second case the capacity is at most at the level of the best competitors on the market.

In conclusion: anything that is above the well established brand names is a blatant lie. Anything that is at their level might be a lie or could be true, no way to figure out than to measure it.

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    \$\begingroup\$ Is there a good site or resource that keeps track of the 18650 capacities as they climb? I.E. will be continually up to date? What I'm looking for is a source for (today's) realistic range of 18650 mAh capacities, kept up to date. \$\endgroup\$ – Ehryk Mar 1 '16 at 10:21
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    \$\begingroup\$ @Ehryk: Not any that I would be aware of, just have a look at the big players datasheets \$\endgroup\$ – PlasmaHH Mar 1 '16 at 10:28
  • \$\begingroup\$ I've recently come across an 18650 database although I don't know how up to date it is. Here's the link: diypowerwalls.com/celldatabase.php \$\endgroup\$ – Levi Roberts Sep 3 '17 at 18:00
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If the cell is actually genuine (no guarantee about that) then it should follow the datasheet. Note that genuine and unmodified 18650 cells are not generally sold through legitimate distributors such as Digikey or Avnet, probably for liability reasons.

Most of the ones you see with unknown brand names (anything with 'fire' in it, IME) will have a fraction to a small fraction of the claimed capacity. Maybe 1000mAh rather than 4000 or 6000 or whatever they are claiming this week. The crap ones will be significantly lighter than the genuine cells, and probably made with inferior materials internally. If you're lucky (and they claim protection) they'll have short-circuit protection polyswitches to reduce the chances of drama. Undervoltage protection is also possible, but less common.

Many of the folks selling these online on eBay, Aliexpress etc. are shady criminals to begin with in that they're lying about the contents of the package and dropping it in airmail. Extremely dangerous practice.

There are websites (probably flashlight related) that do some testing and you will have a better chance if you follow their recommendations. You can also find some cells with protective circuits added from distribution.

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  • \$\begingroup\$ I'm building a battery bank, with 4A polyfuses and my own external protection circuitry, so I'm just after the raw 18650 unprotected cells. It's just hard to tell at what point I'm better with 8x "9,800 mAh" (which might be really 1000 mAh) vs 1x genuine 3,500 mAh - note that I'm still potentially getting more capacity per dollar from the liars, depending on their actual rating. \$\endgroup\$ – Ehryk Mar 1 '16 at 19:38
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At least these are fireproof:

enter image description here

These... maybe not.

enter image description here

Source: fake 18650 teardowns.

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I bought some 9800 mAh Li ion 18650 batteries on eBay and tested them with my genuine SkyRc charger/tester. maximum capacities were between 990 and 1080 mAh each with a sample set of four cells. Yes I was hoping for 2500 mAh, but for two dollars you get what you pay for. Where weight or size is not an issue, you are correct; The liars offer cheap energy capacity at even 10% of the advertised capacity. All the usual caveats apply with purchasing substandard products so good luck. :)

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  • \$\begingroup\$ Welcome to Electronics.SE but this doesn't seem to answer the original question. \$\endgroup\$ – tangrs Aug 1 '17 at 6:46
  • \$\begingroup\$ What is their C rating? \$\endgroup\$ – neverMind9 Jul 6 '18 at 13:46

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