18650 battery resistance SM8124 Battery Resistance Tester 

Fantastic video! Have same SM8124A and love it. Use it to intermittently check solar battery bank of 8S2P Trojan T-105s (6v) for 48v system. I simply let batteries rest a few hours and test each one. Saved my hide once when a float for one of the cells of my watering system (FLA) got stuck and began to allow plates to become exposed. Also, able to test connection resistance of cables between batteries by subtracting the sum of 2 batts in series from the sum of both batts connected with cabling. Temperature is critical and must be constant among all batts when testing, though. Really love your no-nonsense vid; going to check out your other vids now. Thanks, Nexi Tech.

Hi and thanks for the video. Lets say I have a simple 2s2p battery pack. Two cells are 1500mAh and 100mOhm and two are 2500mAh 50mOhm. If I take one of each and make a parallel connection won't I end up with a battery pack that is balanced? (two 4000mAh + 33mOhm in series) It would be great to see how much the resistance can deviate within a parallel group. We know that in series it's very important that it's matched but parallel?

I agree with you on most of this, but not all of it. If you are building a battery pack for a high drain application then yes, performing an ESR test can be valuable to keep your cells balanced. But if you are running something really low drain like a powerwall, ESR can be mostly ignored since the drain on each cell is so small to begin with.

hum... i would totally concur if i was making a high current type battery back to match IRs, but if I was building a low current drain application pack, i would think the IR wouldnt make a significant difference in pack matching. high current, the high IR batteries will drop voltage very fast and get hotter than the low IR batteries. But for low current drain applications, matching capacity would be more important. and in a perfect world matching IR and capacity would be best.

Are there BMSs that can discharge more than 100milliamps? I mean are there BMSs that are better at balancing recycled 18650s that might not stay in balance as well as new cells?

Thanx for video. Essential information. Generally speaking,. What values limits do u deem useable for 18650. I am building a ebike pack for the first time. Want a safe and reliable pack. Thanx

Thx for an informative video. I'm getting ready to build a 20s3p pack using identical cells but with varying condition. Some have a bit higher resistance and lower capacity. My question is, to achieve as balanced a pack as possible should I focus on capacity or resistance first? Every group of 3 cells in parallel should have similar total resistance and capacity, yes? Can I calculate resulting resistance by using 1/R = 1/R1 + 1/R2 + 1/R3 ? So for example I can mix 30+30+30mOhm in one group and have 20+30+40mOhm in another group and still have balanced groups? Thanks!

I think those cells have different c rate..how can you factor that in?..after you match these cells carefully with their IR and capacity, how does each cell behaves when discharging with regards to their different C rates?..do they discharge evenly?..thank you..

thanks for your video. The closer to zero or the lower the resistance the better for the life of a future battery pack, right ??? On my meter which ohm's option do I choose to make this measurement ???

Thanks for the informative video, it was very good. I have a question. It wasn't quite clear from your video about how to use this information. Do I want all the cells in the entire pack to be of very similar resistance, or in each parallel group, or each series group? I'm in the process of collecting cells for a small powerwall (about 4000 cells). Matching resistance will mean a LOT more checking and setting aside a LOT of cells with mismatched resistance. Also, how close should the resistance levels be? 5 or less mili-Ohms, or is a 20+ mili-Ohm difference OK? Thanks.

It shows different resistance values on the charger because contact surface is different each time you plug in the battery. Try applying small pressure to contacts when you plug in the battery and you will get better readings

subscribed/liked...right up my alley!

Always use cell level fusing when creating large packs like the one by the wall.

More about the Anet A6, pls. Great video BTW. Love yourvids

Hi, In your opinion what would be the tolerance value of capacity and internal resistance values to match 2 or more 18650 cells?

Thanks for the video. But what about battery capacity, do we not need also the match those as close as possible?

can you please please please make a video on how to hook up a anet a8 to a pc ! :) :)

Hello,i want to ask a question,does resistance matter if i a am building a battery pack out of 15 batteries and the maximum load on the pack will be about 15A. Each cell can output 4A...so if i have about 1A load on each battery is it necessary for the batteries to have the same resistance ? because buying new batteries would be a big expense for my project....thanks for any answer :D

With the YR 1035 milliometer tester I measured the internal resistance and voltage of numerous rechargeable batteries that I had finished recharging. I wanted these conditions to see the parameters at full charge of all the batteries. I noticed that some of the same make and model have almost the same voltage (varies by a few millivolts) but different values ​​of internal resistance (sometimes even double and triple). This is because some batteries are old, others partially new and others new (an older battery has a higher internal resistance). So the data I have are: internal resistance and voltage at full charge but without load connected to the battery. With these data with which calculation is it possible to know the real charge in Ampere available to the battery? To give an example: two identical batteries measure like this: batt1: 1,2806 volt and 0,0227 Ohm (or 22,7 mOhm) batt 2: 1.3204 volt and 0.0216 (or 21.6 mOhm) How many amps does one and the other battery have inside? Thank you

Doesn't the state of charge matter for these tests? You have a 20ohm resistor in that meter and its drawing power from the battery, lithium battery has high resistance when full or dead but in the middle can be very low. So your going to get varied results depending on how much power is in each battery. Unless your testing each cell at full and again at empty and see what the difference is, the resistance will vary.

Try pushing the negative terminal up with a pencil when you test the cell to apply pressure and a full contact (this should then give you an accurate reading)

If you also know the specs of the cell and what the internal resistance should be from the data sheet. Then you can test the IR and determine if the battery has been abused or has internal shunts in it. In other words if the cell should be 3,000mA capacitor @ 50m Ohms and you measure it at 100 then you will probably find the capacity to be around 50% to 60% or the new cell specs. You can also expect that one to get hatter during charging and discharging. So instead of waisting time charging to see if a cell gets hot I would assume if the internal resistance is 60% or higher then listed in the data sheet it not a gold cell to re-use and you save time on charging and discharging.

Wow 260 cells in that pack he had behind the foam wall lol

Will that tester work with lipo cells? So I can test my drone batteries ?

So a charger with a capacity of 300 mA balance is better then one with 100 mA balance? Can you detail please? The diff between cells must be maximum 100mA ? or why?

Could we add resistance to a cell to balance it with another?

Well it looks good but the numbers in your resistance meter are all over the place! How do you get consistance in a meter that the reading is all over the place?

Which is best for internal resistance Higher or Lower? Thanks

hello, can NI-MH resistance be measured?

Say I want to build a 6S 4P and I have different old cells with different capacity groups off laptops, which ones do I add for the series groups and which ones for the parallel groups ? Meaning is it more important that the capacity is closer in the series groups or in the parallel groups?

"Hi, I have a question regarding the internal resistance of 18650 battery 1- What is the risk of building a recycled 18650 lithium battery without checking and measuring the internal resistance? 2- How is the battery built after measuring and knowing the internal resistance values of the 18650 batteries, especially if the internal resistance values for each battery differ from the others for 18650 for recycled lithium batteries?"

How close should the resistance be to each other?

so there you are hiding your battery packs!hmmm...Nice info there.What is a max number for 18650 internal resistance to use it to a battery pack?for example 150? can be used?And something last as more internal resistance has a battery means is used more so it drains faster?

Do the "10 min Resistance/Capacity Hack for Opus BT C3100" to correct the resistance reading.

I'm confused now can't you just check resistance within normal multimeter

How close an IR do you think the cells need to be? The 85mOhms and 60mOhms in your video that you said can't be in the same cell group but that is only a 0.015 Ohms difference. In that case it appears you are saying that every cell in the whole battery needs to be less that 0.015 Ohms difference? I don't think that is necessary in a 30A to 50A maximum discharge pack that is 6P to 10P made from cells with different chemistry, resistance, and capacity. With different cell resistance you will have different allowable discharge rates. You Sony VCT4s are 13mOhms datasheet and 17mOhms real life. They are 20A high drain cells. So cell Resistance and discharge rate are indirectly proportional -- low resistance == high discharge. So you don't want to be pulling 60A from a 6P battery pack when some of the cells are high resistance and low discharge. So if you have a 6P battery and you use 20A cells like VTC4's and other cells that are 60mOhms and perhaps 5A cells and you draw 60A from the 6P you will harm the 5A cells. So what you need to do in that case is make your maximum draw xP * 5A for 30A maximum. When you are dealing with cells connected in parallel they self-balance when the current draw stops. So when you draw current some cells will have a higher voltage drop due to higher Resistance and during a current draw the higher resistance cells will discharge less energy and when the current draw is removed they will be at different voltages and they will automatically self-balance so that they all have the same voltage. The BMS balancing you discuss is serial balancing as parallel cells self-balance. When it comes to serial balancing it is about having the same capacity in each cell group that is important, way more important that the internal resistance of the cells. With used cells you can use repackr.com for that. But still the internal resistance is important to keep as close as possible because what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different and that is why serial balancing with a BMS or balancing charger is required. When you have used cells you have different capacities, different resistance, AND different chemistries the cells are deteriating at different rates. To think that you are going to be able to keep a battery pack balanced made from cells with different capacities, resistance, and chemistries, you are expecting a bit to much. Also for smaller packs like 13S6P 100mA will work to balance, just the balancing bleed will be a bit slow but you can leave it on over night and it will balance it self out. Of course what will happen is the higher resistance cells will loose capacity faster than the lower resistance cells and your cell group capacity will become different. Now 100mA on your bit battery hidden in the corner that is a different story. Also when you want to group your used cells together into same Ah groups you can use repackr.com which works well for used cells.

I don't really care about internal resistance .. capacity matching is more important for me ...

Any battery, no matter its chemistry, which, if being tested, shows a drop of its original capacity (in mAh) equal or more than 20%, or in other words if you get only the 80% of its original capacity, it's considered as worn out. From that condition onwards, it will not last any longer if you intend to keep using it. Talking about Lithium batteries specifically, no balancer will work perfectly in this condition. The deviation between the cells will always get bigger and growing. When a new lithium battery measures 20mOhm, the rule of thumb is "reject it if it measures the double internal resistance", I.e. 40mOhm. If you'll measure its capacity you will easily understand why is that true. Therefore the best info this instrument can give you, is when to reject worn out batteries, instead of trying to match old ones, at the end of their operational life. Any rechargeable battery with high internal resistance consumes (in fact wastes) energy during both, charging and discharging. Through its internal resistance, in both processes, it transforms this energy in heat, which is nothing but loss of energy. This simply means that a worn out battery can never be fully charged (referenced to its nominal capacitance), while it gets much more quickly discharged if put in service, (because its internal resistance adds to its external load)...Matching worn out cells is practically meaningless and is, in any case and among others, waste of time.

fiy: cheap lipo chargers like the isdt nano can measure internal resistance as well as charge up to 6 li-ion cells

Yep i looked at all of your batteries and i suggest that you throw them away because it's a load of crap. :-))

Sorry but i don’t think your testing device is any good!!! The numbers are all over the place even in the new battery!!!!

With the YR 1035 milliometer tester I measured the internal resistance and voltage of numerous rechargeable batteries that I had finished recharging. I wanted these conditions to see the parameters at full charge of all the batteries. I noticed that some of the same make and model have almost the same voltage (varies by a few millivolts) but different values ​​of internal resistance (sometimes even double and triple). This is because some batteries are old, others partially new and others new (an older battery has a higher internal resistance). So the data I have are: internal resistance and voltage at full charge but without load connected to the battery. With these data with which calculation is it possible to know the real charge in Ampere available to the battery? To give an example: two identical batteries measure like this: batt1: 1,2806 volt and 0,0227 Ohm (or 22,7 mOhm) batt 2: 1.3204 volt and 0.0216 (or 21.6 mOhm) How many amps does one and the other battery have inside? Thank you