guys,

I am interested on some feedback on some tests i carried out on a lithium battery. I wont go into great detail but is it reasonable to be critical to have over 8% of a sample batch of 169 batteries not meet the rated capacity after 4 elevated charge / discharge cycles? - I used charge and discharge rates 25% greater than specified. The rated capacity was ~650 mAh. I monitored temperatures also and the peak temp was bordering 35/36 degrees C. Maybe I am too critical but i would expect them to perform better over such a short test.

 

4 elevated charge / discharge cycles? - I used charge and discharge rates 25% greater than specified.

If you were not using the rated charge/discharge regime, wouldn't that account for the rated capacity not being met?
Were they a reputable brand of battery from a reliable source?

 

huh? You performed a test that doesn't comply with the stated test conditions and are wondering why it didn't meet the specifications?

"Hey mom.. How long does it take to make the cookies?"
"Why that would be 20 minutes at 375 son"
"But I'm confused mom.. I cooked them for 20 minutes and they are burnt crisp"
"Well what did you have the oven set at"
"450"

 

The point being the majority of the batteries performed fine but a large enough quantity to get me wondering did not meet minimum capacity.
The fact that I used slightly elevated rates of course would impact on capacity but I would expect them to last longer than 4 cycles as I have tested plenty of batteries in my time. And no, they were not exactly a reputable source.

 

................ And no, they were not exactly a reputable source.

There's your problem.

 

Well, seems like a combination of factors here, then. (Likely) Cheap batteries from a less-than reputable supplier, exceeding charge/discharge specs..
Are you overly critical? Yeah, I'd say so... Also, 36 degrees for a Li-ion doesn't seem too bad if you're exceeding draw.

 

I think the temperature results are somewhat subjective, (based on results from should I say more reputable batteries I tested lately) If I seen the temperatures remain the same or around the same for much longer I would probably be satisfied on this matter.

I am more critical of the drop in capacity from a very short test script, batteries can run at elevated rates (otherwise they would never pass UN and IECEE tests). The fact that the vast majority did return acceptable values confirmed this matter. I would have expected ALL the batteries to return similar-ish results from this test, having a sizable chunk give back some negative capacities I was immediately thinking of the quality of these and it looked like a degradation in these batteries.

 

guys,

I am interested on some feedback on some tests i carried out on a lithium battery. I wont go into great detail but is it reasonable to be critical to have over 8% of a sample batch of 169 batteries not meet the rated capacity after 4 elevated charge / discharge cycles? - I used charge and discharge rates 25% greater than specified. The rated capacity was ~650 mAh. I monitored temperatures also and the peak temp was bordering 35/36 degrees C. Maybe I am too critical but i would expect them to perform better over such a short test.

What was the expiration dates on the batteries?

 

guys,

I am interested on some feedback on some tests i carried out on a lithium battery. I wont go into great detail but is it reasonable to be critical to have over 8% of a sample batch of 169 batteries not meet the rated capacity after 4 elevated charge / discharge cycles? - I used charge and discharge rates 25% greater than specified. The rated capacity was ~650 mAh. I monitored temperatures also and the peak temp was bordering 35/36 degrees C. Maybe I am too critical but i would expect them to perform better over such a short test.

I take it that charge / discharge cycle is what the product is built to?

 

expiry dates is interesting point. I am not sure (what that date may be)

 

expiry dates is interesting point. I am not sure.

It doesn't make sense for rechargeable batteries to have an expiration date.

 

It doesn't make sense for rechargeable batteries to have an expiration date.

Why? Rechargeable batteries contain solvents to keep the electrolyte in solution (usually a cyclic carbonate - derivative of propylene carbonate).

Polymer membranes and polymer/metal sealing surfaces of the outer packaging allow some oxygen diffusion (unavoidable - cannot be stopped, only slowed). As oxygen diffuses in to the package, the electrochemistry changes - increasing internal resistance and, causing precipitation electrolyte and surface oxidation (With oxygen) instead of no-coordinating ions. Increased internal resistance increasing self-heating on discharge/charge cycle and creates a positive feedback loop - more oxygen, more heat, less performance, shorter life.

Does it makes sense now?

 

Does it makes sense now?

Nope. They have limited recharge cycles, but I've never seen an expiration date.

 

Nope. They have limited recharge cycles, but I've never seen an expiration date.

Seeing an Expiration date on a lithium battery, maybe not. Best used by date on lithium battery, yes.
Does time kill rechargeable lithium batteries, yes.

Tesla knows this too. Tesla knows that recharge cycles only hurt lithium batteries if they exceed the temp that allows excessive oxygen permeation or damage to the electrolyte or excessive solvent venting/pressurization. Tesla batteries are carefully monitored and power is reduced (or charge rate is reduced) if batteries get too warm. Their warranty is only time based - not mileage or charge-cycle based.

https://www.teslamotors.com/blog/infinite-mile-warranty

 

I concur, I have had 'brand name' 18650 cells lie around and was surprised to see quite a few of them 'dead' so to speak after about 9 months of inactivity, there is a chance they were at a low SoC when last used but I recently tried to do tests with them and they were not having any of it.