Different Li-Ion 18650 types.

[Nigel Goodwin]

We use quite a lot of 18650's, both for repairs, and for products we build, and usually buy them in boxes of 100. We normally buy proper Samsung ones from a UK battery supplier, and these are rated at 2600mAH - however, recently (while I was off work following an operation) the supplier notified us that they are no longer able to supply Samsung ones.

They offered an alternative (which I haven't seen) but in the meantime my boss ordered four 18650's from Temu (just to test), at a much lower price, and these claim to be 3000mAH. They have the same pink heatshrink covering, and instead of saying 'SAMSUNG' the label says 'SA SUNG'

Strangely, considering the limitations of Li-Ion, as supplied the Temu cells all read 3.0xV (too low) where the Samsung cells all read 3.5xV (correct) - which doesn't bode well.

However, I've connected them to one of my own designs, as it squirts serial debugging data out of a serial port, and it fully charged the batteries (four in parallel) in 7:55:59, so just short of 8 hours - I like to charge them gently and fully. This is pretty well in line with the Samsung cells, although I've never bothered to write down the charging time for new cells.

Currently I'm running them in the equipment, again taking advantage of the debugging data, and they have been running for about four and a half hours now, and are down to 3.96V - it'll continue after I've left work, and will shut down once it gets to where my software considers the batteries are flat, and I'll check the final time on Monday.

We've still got some brand new boxed Samsung cells left, so I'll repeat the same test on Monday/Tuesday for a comparison.

My concern is the 3V terminal voltage of the cells as provided, as it's below the recommended discharge voltage - what do people think?.

 

[schmitt trigger]

My understanding is (and please correct if wrong) that although a Li Ion battery will not self-destruct like a Pb-acid battery if stored at low voltages for extended periods of time, nevertheless the operating life (meaning the number of charge/discharge cycles) is compromised.

Temu is the poster child for “Let the buyer beware” company. They do have some amazing value stuff, but other things are pure Scheiße.
But at least you’re doing due diligence on these batteries, to have a documented understanding of the product’s quality.

HINT; I know that what I am going to suggest is a lot of work, but if you could duplicate this test after a few dozen of charge/discharge cycles, it would provide additional and valuable insights.

 

[MrAl]

We use quite a lot of 18650's, both for repairs, and for products we build, and usually buy them in boxes of 100. We normally buy proper Samsung ones from a UK battery supplier, and these are rated at 2600mAH - however, recently (while I was off work following an operation) the supplier notified us that they are no longer able to supply Samsung ones.

They offered an alternative (which I haven't seen) but in the meantime my boss ordered four 18650's from Temu (just to test), at a much lower price, and these claim to be 3000mAH. They have the same pink heatshrink covering, and instead of saying 'SAMSUNG' the label says 'SA SUNG'

Strangely, considering the limitations of Li-Ion, as supplied the Temu cells all read 3.0xV (too low) where the Samsung cells all read 3.5xV (correct) - which doesn't bode well.

However, I've connected them to one of my own designs, as it squirts serial debugging data out of a serial port, and it fully charged the batteries (four in parallel) in 7:55:59, so just short of 8 hours - I like to charge them gently and fully. This is pretty well in line with the Samsung cells, although I've never bothered to write down the charging time for new cells.

Currently I'm running them in the equipment, again taking advantage of the debugging data, and they have been running for about four and a half hours now, and are down to 3.96V - it'll continue after I've left work, and will shut down once it gets to where my software considers the batteries are flat, and I'll check the final time on Monday.

We've still got some brand new boxed Samsung cells left, so I'll repeat the same test on Monday/Tuesday for a comparison.

My concern is the 3V terminal voltage of the cells as provided, as it's below the recommended discharge voltage - what do people think?.

Hi there Nigel,

I can guess that 3.0v is ok I think they are allowed to go down as far as 2.5v. They are supposed to be shipped at 60 percent but by air might only be 30 percent.

I have had good luck with the following online stores:
Batteryjunction.com
Batteryspace.com

Over the years I've gotten several batteries from these places (mostly 18650) and they all worked well. Prices vary from about $5 USD and up, but they may have quantity pricing, and may have free shipping for orders $50 USD and up.
I think they sell Samsung, and also Panasonic which is pretty good.

Just recently I took a chance on two 18650's from Amazon, brand "Taken".
I've never heard of that brand before, but some guy did a test on several brands and found them to be near the top. They were two for $14 which isn't really a bargin but I do not need many. They charged as expected, taking a long time to charge at only 500ma, which is a good sign. You can get an idea how good they are that way, at least in the short term.

Long term testing is another story. Some cells (none of mine) can fail after only a few months, but that's probably rare.

Another place to try is Candlepower.com as they have people there that test things like flashlights and batteries, and they do some pretty comprehensive tests.

I use a charger that can charge at 500ma, 700ma, 1000ma, and 2000ma, and normally I do not go over 1000ma. The charger also has a "discharge" function though, which I often use for new batteries even alkaline. I can test any battery to get a real-life capacity test. For the Li-ion cells, I just do it once then charge them again. For the alkaline cells, out of a pack of 40 I just discharge 1 cell that I pick randomly and that tells me if they are worthwhile.
BTW there are many chargers on the market now that can do discharge tests without a separate unit.

What I was not sure of is if you need the flat top cells or the button top cells. Some of these places will weld a button top on for you if you need it and you want to buy a flat top. That's a nice service.
What else I don't know is if you need protected or unprotected is ok.

I just remember I had gotten four 18650's from Amazon one time brand "Sony". They are flat top, and they worked very well. They are high discharge 30amp type.

Well, hope this all helps, if I can think of anything else I'll reply again.

 

[rjenkinsgb]

For DIY use, laptop batteries are a good cheap source of reasonable 18650s

I've been buying such as 7800mAH ones for Dell 1526, from UK suppliers on ebay. Nine decent cells for (last time I bought some) around £12

Those had cells with a part number & I could find the data sheet for them.

 

[Nigel Goodwin]

What I was not sure of is if you need the flat top cells or the button top cells. Some of these places will weld a button top on for you if you need it and you want to buy a flat top. That's a nice service.
What else I don't know is if you need protected or unprotected is ok.

Thanks for the post, not that it really matters, but we use unprotected flat top cells - we weld our own strips on them if required - for the unit I'm testing the cells in, I now use a four way battery case mounted on a small PCB, bolted to the bottom of the case. Previously I welded the cells together, heat shrunk them, and them bolted them down using a 3D printed bracket.

All protection, charging etc. is done in software.

 

[Floyale]

That’s interesting about the Temu cells. The low voltage at the start does seem a bit off—it could mean they’re either really depleted or not quite up to standard. I’ve had similar issues with cheap batteries before; sometimes the performance just doesn’t hold up over time. It’s great that you’re testing them out thoroughly and comparing them to the Samsung cells. If they don’t perform as well, you might want to stick with the reliable brands you’re used to.

 

[MrAl]

That’s interesting about the Temu cells. The low voltage at the start does seem a bit off—it could mean they’re either really depleted or not quite up to standard. I’ve had similar issues with cheap batteries before; sometimes the performance just doesn’t hold up over time. It’s great that you’re testing them out thoroughly and comparing them to the Samsung cells. If they don’t perform as well, you might want to stick with the reliable brands you’re used to.

Hi,

Maybe you did not real the other replies. Another reason for the lower voltage could be due to a safety standard for shipping Li-ion cells when they have to be shipped by air.