Salvage "older" 18650 cells from laptops.

Hi,
I'm just starting the process of building a battery for my soon to be electrified Bullitt Cargo bike.
I got a really good price from a dealer on laptop batteries to be used with older laptops (~11$ each), they contains 8 cells per unit, each cell holds 2200mAh and they are branded cells from Samsung.
The question is, should I go with this? the cells are all made about 4-6 years ago, would age affect the cell much? They are all brand new and never used, it's just an old stock.

The total setup, except for the Bullitt frame will be...
Bafang BBS02 48V @ 750w (if anyone has any thoughts on this, please inform me)
Rohloff speedhub
And the battery...
The shopping list right now is
Bafang BBS02
spot welder
BMS
nickel strips
Something to wrap it in
and some kind of box for the battery.

never used sounds good. cells age over time. sure. can't say how much. this depends on many factors, like state-of-charge, temperature, etc ...but they should be fine.
i would buy one pack and test the cells. max capacity at maximum discharge rate.
then see if they deliver 2,400mAh and see if they are all the same.
also remember that you will need a lot of these cells paralleled if you need some current. those laptop cells are always high capacity and not high discharge. so they sag a lot under load.

No, don't get them.
Used mixed cells will go out of balance quick and be a pita to charge. Also laptop cells are not high c rated so you'd have a big low output pack. I got 40 laptop and tried it. Huge amount of work for little reward, not worth. It even for free imo.

aaronski said:

No, don't get them.
Used mixed cells will go out of balance quick and be a pita to charge. Also laptop cells are not high c rated so you'd have a big low output pack. I got 40 laptop and tried it. Huge amount of work for little reward, not worth. It even for free imo.

Click to expand...

he said that they are BRAND NEW and it sounded to me as if they were all the same.
i would use 25r cells if i needed a high current pack or panasonic ga 3450 if capacity is more of a need.

They are all the same, same age, same brand, same color, same taste.
The max amount of cells I can get hold of with what I know for sure is from the same batch contains 200 cells.

For testing what they deliver, I will need to cylce the batteries, any tips on a good unit?
I have a really good universal 4-Cell Charger & Analyzer charger from Maha, but that's for AA and AAA, is there anything like that in the world of 18650?

Hmm, here's what I think. Start with a decent battery, perhaps only 10 ah. Use this most of the time, when you don't want to go so far.

But then if you desire a lot more range, then a cheaper way to get more is good. What I'm saying is most of the time you won't want to carry 30 ah or so of these cells. The problem with most laptop cells is they are made for lower discharge rates. So 10 ah of it is good for about 5 amps, and your bike can draw 20 amps.

So ideally that laptop pack needs to be 30-40 ah. Huge, heavy, even for a big bike. The cells will have a discharge rate they are supposed to handle. Cut that in half, if you expect the cells to last. Bear in mind, that laptop never drew 1c rate. (about 2 amps for the original pack)

Then, they are old, so if you hammer them, they won't last.

So I'm saying get a reasonably good 10 ah pack now, and ride now. Then if you want more range, you can spend the rest of the summer testing cells internal resistance, sorting, and turning them into a usable pack. And,,, tell that guy $5 per pack. They might be unused, but batteries do age out on the shelf, and they are NOT the cell you'd choose to make a traction battery. They are low discharge rate.

<-----*points at dogman*.

What he said. Much more eloquent.

As my "rule of thumb" with laptop cells, I recommend ≤ .33C - .5C sustained drain with a maximum 1C surge-brief battery drain.
This minimizes voltage sag and damage due to excessive discharge rate.

"Bafang BBS02 48V @ 750w" would have a minimum 20A but more likely a 30A controller.
For a 20A controller, a ≥ 13s10p 48.1V 22Ah
For a 30A controller, a ≥ 13s15p 48.1V 33Ah
Larger than 1C to offset capacity degradation due to age.

13s15p 48.1V 33Ah Lithium battery is about the same size ... but weighs less than half of a 48V 10Ah SLA battery!!!
500% the usable capacity!!!

Note: Ah capacity should be figured by actual capacity rather than the original oem rating.

lots of good information out there on building laptop packs. Dr angle is a great start. There are also lots of new good cells out now. As it takes lots of time building used cells. Doyou have a spot welder ? Don't rip off the tabs if you don't. How are you planing I'm putting the pack together. SSoldering ?

Here's the battery section stickey index
https://endless-sphere.com/forums/viewtopic.php?f=14&t=69683

and heres the DrkAngel thread on laptop cell pack-building
https://endless-sphere.com/forums/viewtopic.php?f=14&t=26383

Question: dogman dan says these batteries are not good for "traction batteries" due to low discharge rate. Is DrkAngel then suggesting that low discharge rated laptop batteries can be made useful as traction batteries if paralleled to create more Ah than A the controller will draw?

Good condition laptop cells perform excellently at .33C - .50C!
They have adequate performance with modest sag at 1.00C.
Extremely briefly, they can surge at 2.00C ... but expect poor performance and rapid deterioration!


Remember though, especially with used cells ...
Battery Capacity >>> C rate should be rated by actual capacity rather the original "new" capacity.

DrkAngel said:

Good condition laptop cells perform excellently at .33C - .50C!
They have adequate performance with modest sag at 1.00C.
Extremely briefly, they can surge at 2.00C ... but expect poor performance and rapid deterioration!


Remember though, especially with used cells ...
Battery Capacity >>> C rate should be rated by actual capacity rather the original "new" capacity.

Click to expand...

Got it.. I think. So once I know the "new" capacity I can ensure .50C discharge by adding enough cells in parallel to accommodate a 30A controller. Is this accurate? Can just keep throwing more parallel cells to solve a discharge problem? Thanks!

Lithium Cobalt (Laptop) cells:
A true .50C = .5C = 1/2C continuous discharge will give you a reasonable, almost, 2 hour run time!
At low discharge rates, Lithium cells are capable of close to 100% discharge efficiency.

Compare to lead acid:
A true .50C = .5C = 1/2C continuous discharge will give you, about, 1 hour run time!
At low discharge rates, Lead Acid cells are capable of around to 50-60% discharge efficiency.

DrkAngel said:

Lithium Cobalt (Laptop) cells:
A true .50C = .5C = 1/2C continuous discharge will give you a reasonable, almost, 2 hour run time!
At low discharge rates, Lithium cells are capable of close to 100% discharge efficiency.

Compare to lead acid:
A true .50C = .5C = 1/2C continuous discharge will give you, about, 1 hour run time!
At low discharge rates, Lead Acid cells are capable of around to 50-60% discharge efficiency.

Click to expand...

Thanks again. So theoretically 0.5C of a measured 2000mAh 18650 cell = 1A. Which means:

• 15 of these cells in parallel getting discharged at 30A would be discharging them at 2C.
• 30 of these cells in parallel getting discharged at 30A would be discharging them at 1C
• 60 of these cells in parallel getting discharged at 30A would be discharging them at .5C

Is this correct? Sorry if I'm hijacking this thread and beating a dead horse here. Note: I realize that the capacity of each cell will need to be measured and to not rely on the manufacture spec when dealing with recycled laptop batteries.

szac said:

DrkAngel said:

Lithium Cobalt (Laptop) cells:
A true .50C = .5C = 1/2C continuous discharge will give you a reasonable, almost, 2 hour run time!
At low discharge rates, Lithium cells are capable of close to 100% discharge efficiency.

Compare to lead acid:
A true .50C = .5C = 1/2C continuous discharge will give you, about, 1 hour run time!
At low discharge rates, Lead Acid cells are capable of around to 50-60% discharge efficiency.

Click to expand...

Thanks again. So theoretically 0.5C of a measured 2000mAh 18650 cell = 1A. Which means:
Wrong ...

• 15 of these cells in parallel getting discharged at 30A would be discharging them at 2C.
• 30 of these cells in parallel getting discharged at 30A would be discharging them at 1C
• 60 of these cells in parallel getting discharged at 30A would be discharging them at .5C

Is this correct? Sorry if I'm hijacking this thread and beating a dead horse here. Note: I realize that the capacity of each cell will need to be measured and to not rely on the manufacture spec when dealing with recycled laptop batteries.

Click to expand...

• 15 (30Ah) of these cells in parallel getting discharged at 30A would be discharging them at 1C.
• 30 (60Ah) of these cells in parallel getting discharged at 30A would be discharging them at .5C
• 60 (120Ah) of these cells in parallel getting discharged at 30A would be discharging them at .25C

Holy crap I finally see it. Thank you!