9900 mAh 18650 accumulator

[FrankBuss]

I bought this accu, ebay seller "toptrade2u":



I charged it with 0.5 A to 4.2 V, then tested it in my electronic load in constant current mode with 0.5 A, and with a turn off limit at 3 V. Result: 400 mAh.



I asked for a refund, no answer so far.

Should I open one? Weight is very light, I guess there is just a small coin cell in it.

[IanB]

I'm curious, why did you buy an "impossible" product, when 18650 cells are typically 2500 to 3000 mAh?

[IanB]

I think you paid too much for them:

https://www.ebay.com/p/925695650?iid=123738605274

[FrankBuss]

Maybe there was a technological breakthrough I didn't notice, and I'm sure I get the money back, so free batteries for at least some low power applications

[FrankBuss]

I think you paid too much for them:

https://www.ebay.com/p/925695650?iid=123738605274

Thanks, I think I should buy them, too. Worth the trouble to give a negative rating so that others don't get fooled.

[SparkyFX]

Out of curiosity: How much weight per cell?

[FrankBuss]

14g. Looks like genuine Sony CT6, with 3000 mAh, should weigh 45g. There is even a seller who claims 12,000 mAh:

http://cgi.ebay.de/371837870210

I just bought it

I discharged one of the 9900 mAh accus completely and opened it. Looks like most of it is air:

[SparkyFX]

With brand names like "ever fire" and "Rakieta" (sounds a bit like rocket)... my trust is very limited :-)
But it reminds me to finally acquire an electronic load, i figure the amount of broken battery packs for e-bikes, e-scooters and so on will either require some refurbishing or at least cheap sources for good batteries. Might need to build a spot welder too...

[maginnovision]

I think they looked at these(similar) on keysights YouTube.

[metrologist]

Here's ya an anecdote. I bought some just like these a couple years ago, plain yellow branded GTF, 9800mAh. I wasn't expecting that, but hoped for something reasonable. I don't have a good means of measuring capacity, but two of them weigh 80g. They power a 12000 lumen, 7 led, 4 cell flashlight for as long as I've needed to use it, like over 2-3 night camping trips, and they're holding a charge a year later, as long as I insert a battery connection block.


https://www.ebay.com/itm/4-3-7V-GTF-18650-9800mAh-Li-ion-Rechargeable-Battery-For-LED-Flashlight-Torch/132466001287?epid=16008260272&hash=item1ed796c587:g:KBYAAOSw-4BXYfqH
https://www.ebay.com/itm/SKYRAY-12000LM-3-Modes-7-x-XM-L-T6-LEDs-Flashlight-Tactical-Lamp-Waterproof/331811563457?hash=item4d4182a7c1:g:xw4AAOSwax5Yx5aZ

[amyk]

Real cells, fake capacities. 400mAh is a normal capacity of cells designed for solar garden lights.

[Circlotron]

They are probably meant for powering things like this 10,000 watt PMPO speaker... 

https://www.ebay.com.au/itm/SMATE-5-1-CH-Dolby-Patented-All-in-one-Soundbar-Massive-150W-10000W-PMPO-HDMI/263119658198?hash=item3d43275cd6:g:g8sAAOSwTQhZgUkA&frcectupt=true

[FrankBuss]

Ok, the fun starts. The seller answered and wants more photos. I sent him the first photo again and described in detail what I did. Maybe I should offer to make a Youtube video, with his shop name and product listing in the intro?

[GeorgeOfTheJungle]

Wow, good stuff!

[FrankBuss]

I don't have a good means of measuring capacity, but two of them weigh 80g.

Might be a good battery, more than twice as heavy as my batteries.

For a rough capacity estimation you could try it with a resistor, for example 10 ohm (needs to be a 2 W type, use multiple in series and parallel, or a higher value, which then needs longer). If the capacity is not that high, this will drain it in a few hours max, so keep an eye on it that you don't deep discharge it and stop discharging it when it reaches 3 V, this should be safe for most 18650 accus. Then use the middle of the discharge curve, 3.7 V might be a good approximation. I guess this is what the "rated" voltage means on the battery. This means it delivers on average 3.7 V * 0.37 A = 1.4 W. If it can do this for one hour, the energy stored in the battery is 1.4 Wh. If only for half an hour, then 0.7 Wh etc. You get the non-SI value "mAh", if you divide the energy by the rated voltage, so 0.7 Wh / 3.7 V = 0.19 Ah = 190 mAh. There is even a webpage for it:

https://milliamps-watts.appspot.com

Or measure the current your flashlight needs and measure the time until it is dim. But could be tricky, if it uses a switched-mode power supply.

BTW, I just verified my electronic load with a power supply, and it uses always 1 V as the rated voltage for battery capacity measurement. Misunderstandings like this happens, when you use silly units like AH. Couldn't find anything in the manual how to change it. So the reading "0.4 AH" means the battery really has 0.4 * 3.7 = 1480 mAh (or maybe a bit less, if the average voltage is lower), because it assumed 1 V, and not 400 mAh as the display suggested. Still about 7 times less than what was sold.

So a recommendation: don't buy the RK8511 electronic load. The capacity measurement is useless, unless I missed something how to change the unit, because it should really measure Wh. I verified it with a power supply to be sure: it shows the same value, 0.0168 AH, when using 9.93 V with 1 A for a minute, and 4.939 V with 1 A for a minute, it just ignores the input voltage, and the entered cut-off voltage. Useless. I guess this is why the seller got suspicious, it can't be that bad

[FrankBuss]

Ok, I think I was wrong with my conclusion that the battery has 1480 mAh and not only 400 mAh. As I tested, my electronic load shows the same mAh value for different voltages, if current and time is the same, because it integrates just current over time. This means the accu has really only 400 mAh capacity. Would be still nice if the electronic load could measure the real energy and not just this mAh approximation.

[Kilrah]

Well since the cells are rated in mAh then the mAh count is what you want to dispute the claims.
But yeah having Wh as well is more flexible.

[FrankBuss]

Well since the cells are rated in mAh then the mAh count is what you want to dispute the claims.

That's right, but it is not very accurate. They would need to specify the cut-off voltage. But below 3V is not much charge left anyway, so I guess it should be within +/-10% of the mAh printed on the cell, no matter if the manufacturer deep discharges it to get a value as high as possible, or uses a slightly higher value than 3V.

I will setup the serial port interface when I have some time, then I can read the voltages with a script and draw a nice discharge curve. And with the raw voltage values it is easy to integrate it for the real energy, because the current is constant.

[IanB]

For a rough capacity estimation you could try it with a resistor, for example 10 ohm (needs to be a 2 W type, use multiple in series and parallel, or a higher value, which then needs longer). If the capacity is not that high, this will drain it in a few hours max, so keep an eye on it that you don't deep discharge it and stop discharging it when it reaches 3 V, this should be safe for most 18650 accus.

I have often done discharge tests with a resistor. If you log the voltage during the discharge you can plot a graph of voltage against time, and thus current against time (you know the resistance).  Then you can find the area under the graph to get the capacity. For improved accuracy I measure the resistor value under warm discharge conditions.

[wraper]

Stupid deal, for such price you can buy genuine 3350 mAh  panasonic ncr18650b.

[Bud]

@FrankBuss you are a valued and experienced person. How could you possibly fall to 9900 mA/h trap. Technological breakthroughs do not originate in China. Unless you just having educated fun.

[SiliconWizard]

Ahah! Sure 9900mAh was next to impossible... but... 400mAh for 18650 Li-ion batteries? You bet they are almost just air!!

[FrankBuss]

@FrankBuss you are a valued and experienced person. How could you possibly fall to 9900 mA/h trap. Technological breakthroughs do not originate in China. Unless you just having educated fun.

You can never be sure. It could have been some new advanced graphene nano particle accu

But to be serious, China catches up quickly in technology. They were the first who landed on the dark side of the moon. And they plan to be the world leader in AI research. And I think they are already world leader in facial recognition, surveillance technology etc., probably "better" than NSA.

[PlainName]

For a battery load tester, you can do a lot worse than an EBD-M05:

eBay auction: #283107190979

[Circlotron]

@FrankBuss you are a valued and experienced person. How could you possibly fall to 9900 mA/h trap. Technological breakthroughs do not originate in China. Unless you just having educated fun.

You can never be sure. It could have been some new advanced graphene nano particle accu

But to be serious, China catches up quickly in technology. They were the first who landed on the dark side of the moon. And they plan to be the world leader in AI research. And I think they are already world leader in facial recognition, surveillance technology etc., probably "better" than NSA.

World leaders in fashion too.
https://www.google.com/search?q=china+accordion+pants&prmd=isvn&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiBqoD0iIHlAhV-7XMBHadZDYAQ_AUoAXoECA0QAQ&biw=1024&bih=675#imgrc=OMEwIvEdapmSZM