How to test cycle life of battery ?

[ichiban]

I admire those who really test batteries for real like thunderheart, Pajda and others that I do not mention here. Especially that they also made that results available to the public. My salute to them. :thumb: :thumb: :thumb:

Actual / straight forward cycles test by charging and discharging to 500 cycles for Li-Ion (or 2000 cycles for LiFePO4) is prohibitive unless you have 24/7 and 3-4 months to do it. Not even the sellers will do it, if they do not really have to.

Is there any easy / credible way to test cycle life of a battery ?

Anyone ?

 

[DogDipstick]

See how much more you put in than take out.

 

[john61ct]

With the right gear, you just set the top and bottom voltages, charge & discharge current rates, and how many cycles, all the data saved for graphing on a PC.

2-3 months at slow rates, that many weeks if high currents.

But yes, extrapolation (guesstimating) is widely used both by vendors and in academia, I'm sure a lot less accurate than actually running the cycles.

Relevant thread https://endless-sphere.com/forums/viewtopic.php?t=103013

 

[DogDipstick]

Look at this. This is a 14 hour log, two cycles from storage voltage to charged. 1/2 hour cool down. 0.5C, ( a relatively small current) ~30Amps. I could do this twice a day, for four cycles per day.

The charger has two settings for cycle life determination. One is a 10 Cycle, the other is a 20 cycle. Configurable to a 10 hour cooldown max. I use 1/2 an hour cause that is usually enough for me to see resing bvoltage.

It would take me 3 full days to run a 10 cycle test. The datasheet specifies cycle life loss data at 60-70-80-90 cycles. This would be ~ 30 days of log on this cell. The cell is ~60Ah lithium.

However, I have tested many cells, and the ones that are old, are beat, are puffy, all put more in than take out on every log with any data, regardless of the current rate, even though that does make a difference in itself.

 

[DogDipstick]

Now, that cell is a used cell, from what we gather. Here is a confirmed NEW LiFePo cell, also rated 60Ah, tested with a 30A current (0.5C).

I tested this cell extensively, and couldnt get non repeatable results. Took 60.4Ah out, Put 61.0Ah in. Less than 1.001% of the final cell capacity. Lost in the charge. Many times it was less than 500mAh... that is under 1% lost to heat during charge.

 

[DogDipstick]

Here is a beat up "8Ah " Headway LiFePo. Trash. Ah? 6.509 out. In? 7.3Ah. in. Lol. On a "8Ah" cell. That is 11% loss. Plus not anywhere near a rated capacity.

 

[DogDipstick]

Here is a beat up "8Ah " Headway LiFePo. Trash.

Ah? 6.509 out. In? 7.3Ah. in. Lol. On a "8Ah" cell. That is 11% loss. Plus not anywhere near a rated capacity.