Some bogus batteries are very easy to spot. Any Li 18650 batteries that claim
3550mAh are definitely bogus. This is because Panasonic is the only company
that has been able to manufacture an Li 18650 battery up to 3550mAh capacity
- but not above - and the cost is more than $20.
One link I found was: 3600mAh 18650 Li-ion Orbtronic, which claims: "Panasonic inside." This is pushing the truth even if it is a Panasonic inside, for which there is no proof. See the letter from Dennis Malec, a Senior Applications Engineer at Panasonic USA, which is at the bottom of this page.
When evaluated on a Capacity-to-Cost rating, the Panasonic 18650 cell comes out very low on the scale. So, unless you really have a need for this much capacity in an 18650 package, it would be more cost effective to select an 18650 cell with a higher Capacity-to-Cost rating, even if you have to change batteries more often.
I acquired a number of Li 18650 batteries that claimed 4000mAh and others claiming 9800mAh. None of these are valid because, as stated above, the best chemistry to date in an 18650 case can only supply a capacity of up to 3550mAh. While this means there are a great many false claims being made on the Internet about such 9800 or even 10000mAh 18650 cells, it may also imply that many manufacturers claiming any value capacity may be exaggerating. For all we know, even batteries claiming even less than 3000mAh may be exaggerating their capacity. The only way I know to evaluate the capacity is to buy some batteries and test them.
I tried a few quick methods to figure out which were bogus batteries and came up with three methods which, while not perfect, can help.
The first method, stated above, is that any seller claiming that the 18650 they are selling is better than 3550mAh is selling a bogus cell. The second method is to come up with a weight to capacity value. However, due to differences in case weight, internal safety circuitry, and other factors, it proved too variable to come up with one average value. That said, the weight guideline can help. When the 9800mAh batteries arrived, the first thing I noticed was that they weighed considerably less than some 3000mAh and 3400 mAh batteries I had.
A 3400mAh battery I had weighed about 47.7g and delivered 3140mAh. Four 3Ah batteries all weighed about 44g each and delivered between 2200 - 2300mAh. The bogus 9800mAh batteries weighed only around 25g.
Using this admittedly-limited example set of batteries, I came up with this general set of assumptions and conditions: I assumed the case weighed about 12 grams and the chemistry is everything else. Using the 25 grams for the bogus batteries, this gave 13g for ~550mAh. So 1g delivers about 43mAh. This means that a 3000mAh battery should weigh ~ 12g(case) + 70g, for a total of about 82g. You see why I'm saying this didn't really work.
However, what did help was weighing all new batteries and testing them to characterize their capacities. The table below shows the mAh VS total weight that came out of those measurements and tests: (The casing and circuitry weight was not subtracted.)
Capacity (mAh) vs. Weight
The basic method for using the weight is simply that if the cell weighs less than 40 grams and claims 3000mAh it is probably bogus. If the claims are for a cell above 3000mAh, then it is definitely bogus. So, the second method is to ask the seller the weight of one cell in grams.
A third method is the cost of the cell. Eight of the 9800mAh batteries delivered 560mAh and cost $13.66 or about $1.67 each. The EBL 3000mAh batteries delivering ~ 2250mAh cost $3 each. The IMREN 3500mAh battery delivering 3150mAh cost $8. So if we look at it this way and rate them on mAh delivered per $1, we get the following table:
Capacity (mAh) vs. $1 Cost
Note: Click the Blue underlined Name in the table above to see the battery capacity test curves. These curves were generated by a Computerized Battery Analyzer (CBA IV) available at Westmountain Radio This is where I bought my basic CBA IV.
Note: The best 18650 battery was (is?) produced by Panasonic 18650 at 3550mAh and the cost I found was ~$22. This Capacity vs Cost is ~164 mAh/Cost. (See the Red information & table entry above.)
Note: The prices quoted in the table are the prices I paid for the batteries alone. No shipping fees were included. Including shipping fees would also be a viable, and perhaps better, way to determine the best mAh for the money spent. Also, your costs may differ, for better or for worse.
So, looking at simply the cost of a 3000mAh cell we can see that anything less than $3/cell is probably bogus. What is surprising is that the EBL cell only delivers between 2000 - 2270 mAh, and yet, its mAh/1$-cost rating is the highest available of the cells I've purchased, at this time.
I purchased an 18650 Li battery claiming 3500mAh. Using a draining current for a 10-hour test, this battery only produced ~ 3140mAh, or about 89.8%. At the standard characterizing test current of 1/20th the rating capacity, or 175mA, the results were between the 1/5th and 1/10th rates. I selected the best, the 1/10th test, to characterize this battery. Cost was $8.00/cell. Other 3000mAh batteries from this company were $6 - $8.
When I approached the seller with these results he said, "The cell is not considered defective if it is not DOA. Once the cell is used, there isn’t a warranty provided either." - Jason from IMRbatteries.com.
Questions about whether this is acceptable or not are not going to be addressed here. The company I bought this from, IMRbatteries.com, thought this was perfectly acceptable and did not make any offer to address the situation.
On the other hand, I also bought 18650-type batteries from another company I found advertised on Amazon. They were claiming that their batteries were 3000 mAh. When I tested these batteries and sent proof that these batteries only delivered 2200 - 2300mAh, this company offered me a full refund or replacement for the problem. The cost was about $3/cell. See the EBL entry in the table above. If you're interested in this battery, go to amazon.com and search on, "EBL 18650 Battery Lithium-ion 3000mAh 3.7V" to find a number of different offerings.
There are so many batteries out there that do not meet their own published capacity claims that it is up to the buyer to find a company that will support the batteries. By that, I mean that the seller will either deliver a battery that can be tested and meets all the advertised claims, or will offer a refund.
How would someone be able to tell a bogus battery from a real one, based on what one can read on the Internet? Unfortunately, there is no definitive way to do this for every possible battery advertised. Some quick ways to tell the really bad from the possibly good batteries were given above.
The first: If the statement claims to supply a battery of type 18650 with more than 3550mAh capacity, it is bogus. There is no such thing due to the limits of the package size (18mm diameter X 65mm length) and the Li chemistry we have today.
The second: Ask the seller how much the cell being advertised weighs. Then use the table above to evaluate the cell. This "rule" is not perfect but it does help. Remember to specify that you want the weight of one cell.
The third: Look at the cost of the cell. Any cell of 3000mAh or more that costs less than $3 is bogus, unless it is a known good cell on some super sale.
I hope these methods will help you to quickly evaluate which cells to stay away from.
I'd like to end with an email I received from Dennis Malec of Panasonic Corporation of North America: