How is capacity wear rated?

[Storx]

I am about 80 cells into my collection of old laptop cells for capacity testing and i had something pop up that made me curious how the rest of the life of the battery will degrade....

Example, i have a good chunk of 2600/2800mAH when new batteries testing around 2100-2300, so using an actual battery i tested: Sanyo 2600mAH cell testing out at 2205mAH, so that is 15.2% roughly of loss capacity..., but then i have a samsung 2200mAH cell testing out at 1843, which is like 16% loss roughly... which one will degrade faster? or will they degrade at similar % of loss per a full cycle... ?

 

[dogman dan]

Flip a coin.

 

[DrkAngel]

I've been building packs from recycled laptop cells for almost 8 years.

Same brand-model cells of varying actual capacity placed in parallel do deteriorate at the same percentage rate ...
when based on present capacity.

2400mAh cell in parallel with 2000mAh cell will equally deteriorate to 1200mAh and 1000mAh.
C rate deterioration seems related directly to actual, rather than original, capacity.

 

[999zip999]

You are building a high parallel low amp battery. So watch your controller.

 

[Storx]

I've been building packs from recycled laptop cells for almost 8 years.

Same brand-model cells of varying actual capacity placed in parallel do deteriorate at the same percentage rate ...
when based on present capacity.

2400mAh cell in parallel with 2000mAh cell will equally deteriorate to 1200mAh and 1000mAh.
C rate deterioration seems related directly to actual, rather than original, capacity.

thank you, that is what i was wanting to know.

 

[dogman dan]

But you asked about different brands. This is why I said flip a coin. Only by testing and finding out can that question really be answered.

I would build the pack so that when you parallel some sanyos with samsungs, make it easy to split out one brand or the other. Like make two packs, one Samsung, one sanyo. then parallel them. This way you can tell which one fails first, and chuck it when you need to.

 

[DrkAngel]

Each bank should have an equal sampling of each type cell ...
Large pack, limiting output to ≤1C maximum output recommended for reasonable life.
EG 30Ah actual capacity Battery if 30Ah controller.
Base C rating on actual capacity rather than original rated!

Limit "tighten up" voltage range for extended life.
Typical Laptop cells are effectively "empty" near 3.70V and reasonably "full" notably below 4.20V. (Static voltage readings)
It is nearly universally accepted that lowering charged voltage will greatly extend usable lifespan!

See- Optimal Charge Voltage

I use Capacity Mapping to determine optimal charged and discharged voltages.
Limiting charged\discharged voltages to regions of good energy density.
This varies with different chemical formulations.
Some are optimally charged to 4.15V but others to as low as 4.05V.