Aliexpress 24V 100AH battery horrible internal resistance.

[Luk88]

So I got the cheapest 24V 100AH battery on Aliexpress that is in stock in Europe to make a small secondary system(replacing lead). Sadly I discovered a video by a Russian guy who bought a 600wh power station from the same brand and discovered it is actually 300wh. So I didn't have high hopes.

Still I decided to test it fully.

The battery arrived almost fully charged, which was very strange as they should not be stored for a long time like this. The voltage read 26.9V. It took about 5 minutes at 30A to charge to 3.6V. Then once the voltage settled to about 28V I tried 1.3kW load through the inverter (the inverter is well tested) and the voltage at 100A dropped to 22V at the battery terminals! 6V at 100A! That's like 60mOhm. It should be 10 times less.

So then I charged it up with a PSU. This time to 3.6V per cell (wanting to avoid high voltage cutoff at 3.65V) and the plan was to check capacity with my 185W load tester. I'd love to be able to do proper 0.2C discharge, but at this voltage the best it can do is 6A.

It also shows the internal resistance of the battery. Which it initially showed at about 20mOhm growing to 150mOhm within minutes.... At 6A!?!

I'm not sure I'll wait the 16h it takes to complete the test. I might charge it up again and discharge with a known load through the inverter so I can send it back sooner rather than later.

My question is, has anyone else encountered this? I expect half the size, but not internal resistance worse than my old lead acid...tue weight is correct. The price is lie, but not outrageous... Also reviews are good. So, I don't know what to make of it.

Edit: Also I asked the seller to send me the battery spec sheet and it says internal resistance <= 500mOhm WTF?! Is this common? In this case it is certainly within spec... But at the same time it says max continuous discharge 100A and max surge 200A.

 

[hwy17]

The answer with internal resistance is always that your testing equipment is neither good enough nor calibrated to be accurate.

 

[Luk88]

The answer with internal resistance is always that your testing equipment is neither good enough nor calibrated to be accurate.

Seriously at 6V voltage drop? One could argue over milivolts, but not at 6V!

 

[MattiFin]

Cheapest battery on aliexpress is not a great start.
There is no lower limit on what kind of crap they sell on aliexpress. Plenty of professional con-artists there that are good in convincing ali customer support that YOU are at fault.

The seller and aliexpress itself is just going to spin you in endless loops, consider escalating this to your credit card company. Your account and/or credit card probably gets banned on aliexpress but as this was probably considerable amount of money it is probably worth the hassle.

 

[Luk88]

Cheapest battery on aliexpress is not a great start.
There is no lower limit on what kind of crap they sell on aliexpress. Plenty of professional con-artists there that are good in convincing ali customer support that YOU are at fault.

The seller and aliexpress itself is just going to spin you in endless loops, consider escalating this to your credit card company. Your account and/or credit card probably gets banned on aliexpress but as this was probably considerable amount of money it is probably worth the hassle.

This item "enjoys free returns" so my money is not at risk (I hope). It's just some time wasted and some astonishment gained...

I thought, half of a capacity, that's easy to detect and is understandable, but such high internal resistance? It is linear too. It's not just at 100A. At 60A I have a bit over 3V drop. This is at 13C BTW. The temperature raises as I'm discharging it. At this internal resistance there must be 180W of heat being generated inside. I'm watching it with a thermal camera BTW... But so far I'm just seeing the side wall getting warm. And brass , yes brass, lugs.


I've discharged 333Wh with the little 180W load. Then the voltage dropped to 26V during the 6A discharge and raised to 26.3V when it stopped. So I connected my inverter and plugged a 62A (battery) load. It has been running for last 15 minutes. During this time the battery voltage increased by 0.3V. This is going to be fun. I wish I still had access to an industrial x ray inspection machine I used to have years ago. I'd love to see what's inside, but I'm not sacrificing $413 (that's what I paid)

 

[hwy17]

What are the test leads/wires like?

 

[Mattb4]

One nitpick. Aliexpress is not the supplier of the battery. You should name the brand and company you bought from.

Yes you should charge it up* and conduct a load test. Likely it will be at 80% of rated. If it is less it would be a good time to see if a return is possible.

* Charging requires taking it up to CV and giving it an absorb time.

 

[Luk88]

One nitpick. Aliexpress is not the supplier of the battery. You should name the brand and company you bought from.

Yes you should charge it up* and conduct a load test. Likely it will be at 80% of rated. If it is less it would be a good time to see if a return is possible.

* Charging requires taking it up to CV and giving it an absorb time.

I will if I establish beyond reasonable doubt this is not a faulty unit. I don't want to slander a honest seller because he sold a faulty product.

I have a technical question. Let's say a battery indeed contains cells that seem the correct size and weight to be 8x100ah cells. Everything is internally connected correctly, no loose wires etc. And cells are made let's say up to a year ago, so not old. Not bulged. We engage in a hypothetical here. Is there some reason why cells would have very bad internal resistance but when discharged very slowly test at good capacity? Also let's assume two strings of 8 measure the same voltage drop so it is not a case of one bad cell.

Could there be anything one could do to "revive" them? Also, what is the probability one could encounter 8 such bad cells nicely balanced in one device without the sellers knowledge? Although seeing that spec sheet with 500mOhm internal resistance I think, it's a strange coincidence to have a mustake like this and it realise I'm the product. Isn't it?

Coming back to my test. The 60A load run for 50minutes until the inverter's undervoltage cut off activated. I measured 21v at battery terminals. The moment it cut off the battery sprung back to 24V and it is still going up (25.05V as I write it now). I've discharged a total of 1400wh so a little over half capacity.

 

[Luk88]

What are the test leads/wires like?

The inverter is connected with 70mm2 (awg3 ?) 2m long leads with crimped copper lugs on ends. Test leads are awg 22, about a meter long connected to hp 34401A bench top multimeter.

Also, let's say the cells heat up during 50A charge sufficiently to be ~30C in about 5 minutes. What would you say to this?

 

[wpns]

Maybe the internal wiring is (very) substandard, or there are other internal connections with a lot of resistance?

 

[Luk88]

Maybe the internal wiring is (very) substandard, or there are other internal connections with a lot of resistance?

I very much doubt it. If it could drop that much voltage it would generate 300W of heat during 100A load. I would see it on a thermal camera, but all I see are cells (also I can tell their size 220*80*50 mm or so, 8 of them, they are visible only on the short edges. the BMS is mounted on one of the long edges - it is not getting too hot).

It is 2am here... and I already spent way too much time on this than I should, but I have some very interesting findings.

For one, does anyone have any idea why it would take an extremely long time to get from 3.45V per cell to 3.55V per cell? 3.45 should be close to 90% This should really be last 10~5% of charge, but it took me almost an hour at 50A (1400W). Then the remaining 3.55 to 3.60 was again 15 minutes and then from 3.6 it started increasing very quickly so I set the charger to hold on 3.63. There it sat consuming 20A! Isn't that a lot for a 100ah 8S battery? It sat there for good 15 minutes dropping slowly to 0. Once It did drop to zero I left it to drop to 3.4V per cell with all loads off. And then I tried my 100A load again. This time the voltage dropped only 3.6V (for the whole battery, previous voltage drop at 100A was 6V, now the battery is close to 40C temperature though) so what internal resistance dropped almost by half to 36mOhm? and when I switched the load off it recovered to 3.32V per cell. Then I engaged the 100A load few times for 5 minutes each time and every time the drop was only 2.818V per 100A or 28mOhm.

Can someone tell me if it sounds reasonable the temperature difference can be responsible for this? From 13C and 60mOhm to 40C and 28mOhm ? Or did this very strange extended charging session have anything to do it and somehow "woke up" these batteries? Is such a thing even possible with LFP? Look, if it was charging and I can drop it by half twice again... I could have a usable battery. If it was the temperature, I'll know tomorrow when it cools down.

This is not my first Lifepo battery. I'm currently building a 16S 280AH battery with Higee cells and believe me when I say the charging behaviour of this is extremely different towards the upper voltages .The Higee cells get up from 3.4V to top voltage pretty quickly, these cells took a very long time and a lot of current, (with solid 50A of current). If this energy was simply wasted it would've boiled these cells very quickly. It definitely was charging. I'd love to believe this battery can be "fixed", but it may very well be the temperature is simply responsible for the brief better performance.

 

[wpns]

Maybe the chemistry came out wrong that day at the factory and they shipped them anyway? Try fully charging till it hits the 'upper' knee and then fully discharging till it hits the 'lower' knee (without knowing ahead of time what they are), and maybe you'll find it's a bunch of (say) 3.5V nominal cells instead of the expected 3.2V nominal.

 

[Brucey]

Due to issues with cell balance it's not uncommon for a battery to need a few cycles before reaching max potential. Some batteries with passive balancers may need weeks...

 

[Luk88]

But could this explain the high and then lower (but still an order of magnitude too high) internal reistance? I guess faulty production could explain anything, but I'm interested in anyone actually encoutered cells that behave like this.

 

[wpns]

But could this explain the high and then lower (but still an order of magnitude too high) internal reistance? I guess faulty production could explain anything, but I'm interested in anyone actually encoutered cells that behave like this.

Maybe the internal resistance is so high because they are nearly discharged. Try feeding them current till the voltage rises without worrying what the absolute value of that voltage is.

 

[740GLE]

Does the BMS allow you to view each cell voltage?

I’d say open it up and watch each cell voltage, find your voltage drop.

 

[Mattb4]

I will if I establish beyond reasonable doubt this is not a faulty unit. I don't want to slander a honest seller because he sold a faulty product.

...

Not to worry Chinese seller and honest are mutually exclusive concepts. It depends on what they think makes them money and if they are forced into it. If you are unhappy with your purchase return it. I have little doubt that it does not meet the 100ah rating.

 

[Luk88]

Maybe the internal resistance is so high because they are nearly discharged. Try feeding them current till the voltage rises without worrying what the absolute value of that voltage is.

I did eventually manage to have the current to drop until my inverter decided it is charged (probably around ~5A).

Does the BMS allow you to view each cell voltage?

I’d say open it up and watch each cell voltage, find your voltage drop.

Yes, individual cells during discharge behave very similarly.

I nw peculiar thing, why I had to set the charge at 29 and no more is because the first cell reached 3.67 while the others were around 3.55 etc. After the current dropped to zero it equalised substantially. I can't understand how the BMS let it get to 3.67V perhaps they were damaged by overvoltage?


I think there is very little hope for this battery. The purpose of this thread is more of an investigation into what of mode of failure results in very high internal resistance, but has remaining capacity.

This morning I went back to see the battery and it cooled down to 16C on the top and 20C where cell ends are. The measured internal resistance this time was 38mOhm at 100A. To further picture how insane that is. When one puts 100A load on it individual cells are at 2.8V from full...

Also it is as if the battery lost some charge. I wanted to top it up (I did the 100A load for about a minute) and the charger run at 50A and 10 minutes in it still hasn't finished fully (it was at top voltage, but the current was still 50A).

So I decided to run the 6A capacity test to its end. I reset the load and I let it run. We'll see if it comes close to 100ah.

Edit: Also I wonder. I cannot find any 100ah cell online with these dimensions :220x80x53. Is it possible these are "special" cells meant for very low discharge currents?

 

[Luk88]

Just to add to this. I found unused lifepo cells that are stored for very long in elevated temperatures mostly degrade by loss of "cyclable lithium". This is a scientific article that describes what happens when a cell looses its "cyclable lithium" https://www.mdpi.com/1996-1073/12/22/4386

It looks very much like what I'm seeing... For example the charging curve shown there, the discharge that shows huge voltage drop etc.

So the most likely answer is: these are correct capacity, possibly unused, but improperly stored very old cells. If anyone has a better idea, please do let me know

 

[Luk88]

I'm replying to myself rather than editing to make sure people that have seen this don't miss this info as it is rather important.

I've discovered almost every single cheap 12/24/48v battery available on Aliexpress in Europe currently is the same scam.

It is called "ampere scam" and it basically means you do get the capacity, but only if you discharge at few hundred Watts tops(a couple amps). How do I know this is not just one seller? Because I reviewed all available battery offers and they either do not state internal resistance or where they do they outright tell you it is 200mOhm. The best I found was 60mOhm. This makes maybe 30% of the capacity usable at let's say 1kW plus on 24V.

So, It seems with the lack of current availability of 100ah cells I'll be staying with lead for some time in my 24v system.