Extended use 18650 battery degradation data - 9 years of very hard use - 12% loss…

[wweiss]

For the general interest of the Forum…

I bought 7,000 18650 batteries in September of 2013 and have used all of them every day, very hard since. Over the course of about 9 years, they have degraded about 12% from original max capacity, after lighting up many thousands of miles of dark country roads.

I thought this is interesting data…

 

[turbodog]

Ahem... pictures...

 

[wweiss]

The lights are located on the right side of the unit, opposite the boat…

 

[Duster1671]

How many cycles have you put on these batteries? (A cycle being defined as a full discharge followed by a full charge.) What was the typical charge and discharge rate for each cell?

I've done bench testing with individual 18650 cells and found that they track very closely to the typical manufacturer spec of 80% capacity after 300 cycles.

 

[turbodog]

Ah. I envisioned some sort of homebrew area lighting for nighttime utility work or something.

 

[wweiss]

Sorry, Turbo… it was a cheap trick on my part.
But Duster poses a good question. The 7,000 batteries do not all discharge in parallel so there are many at the end of a typical day that remain unused as I don't drive until I'm down to zero and then charge fully. The cycles are spread over the 7k cells and they are not discharged completely either - the load is shunted to the next section (see photo of a pack with separated trays of cells)

I can't answer Duster's question. But I do know that overall my range has dropped 11-12% since new. And I have a lead foot.