18650 lifecycle data

[dekes1]

Last year I ran two battery packs, both 14s10p built from salvaged laptop 18650 cells. As we get closed to spring here, I decided to do some maintenance on the packs in preparation for the riding season. While I had them somewhat disassembled, I tested a handful of the individual cells to see how they've held up. I thought I'd share my results here.

After about 750 miles of riding, the batteries showed the following drop in capacity
Samsung 26E - From ~2200 down to 2050
Samsung 28A - From ~2350 down to 2150
LG 2600 From ~2300 down to 2000
LG 2200 From ~2150 down to 1900
Sanyo 2600 From ~2300 down to 1900

On a side note, I've disassembled over 600 laptop packs, and hand charged/discharged and categorized every cell. I've built 6 high capacity packs and of all the cells, I've had only 3 sony US18650GR cells that were worthwhile. I'm not talking about the VTC4 or VTC5 cells, only the lower current laptop varieties but yes only 3 good cells out of hundreds. The samsungs far and away had the best ratio of good to bad

 

[ecycler]

How many cycles over the 750 miles? What were the charge/discharge rate and average voltage levels that you used?

 

[dekes1]

My controller is set at 45A max draw, but i would say on average i only hit that a few times each ride. Most of my riding is hard packed trail and not a ton of high-current off-roading. Even my full speed runs only pull max amps for a few seconds.

I was usually running down around 12-14Ah per ride but usually keeping the pack above 3.4v per cell (I dont have a hard LVC). I was charging to 4.19v at 10amps (1.0a per cell).

I don't know the exact cycle count, but with moderate accuracy i'd say 24-31 cycles.

I've invested in a Cycle Analyst for this season so i hope to capture detailed battery usage stats.

 

[ecycler]

I don't play a lot with these types of 18650's. My current packs for bikes and eskate are either: Panny NCR18650PF, Sony V, or VTC4

However, that does seem like a heck of a lot of capacity loss for one season to me given the data. Did you control for ambient temp during the before and after tests? You may be charging them too quickly... Are you running a BMS and or checking balance and balancing periodically? Thank you very much for sharing your info. I really wish there were more people sharing their data like this for learning from each other's experiments. I am guilty myself of not being meticulous enough with all the time and money I spend on buying/building and destroying cells in the science and art of my blended pursuit of transportation and hooliganism.

 

[dekes1]

Fortunately i work for a Fortune500 company that goes through laptops like candy bars so i can get old batteries relatively easy. On the flip side, i'm at the mercy of used, abused, over-heated, over-discharged and generally poorly taken care of laptops. For my purposes, i consider any cell with greater than 2000mah to be useful and with that criteria i find about 1/3 of all cells are good, 1/3 between 1500-1900mah, 1/6 between 1000-1500 (useful for non-ebike projects only) and 1/6 completely unusable. My experience is that in general Samsung is tops, LG second, Panasonic third, the newer Sanyos fourth and the Sonys and older Sanyos last. I can build an igloo with the number of dead Sony/red sanyo cells.

Sadly, i've never seen a laptop battery with high current cells so unless i buy my own, i'll never have a bulk pack made with high-end cells. The downside being that i need to run a rather large parallel set to get decent amperage.

 

[ecycler]

Do/did you measure the IR of the batteries in addition to capacity?

 

[dekes1]

No, unfortunately my chargers do not have the ability to measure IR. I have an iCharger 308 Duo on order now though...

 

[Skrzypas]

I've disassembled and tested about hundred of batteries (600 cells) and similarly noticed that Sony cells are almost never good to recycle. But in opposite to dekes1 the same was with LG cells for me. Sanyo and Panasonic similar, Samsung the best.

But it doesn't mean Sony/LG are worse. Maybe they are highest quality and they die all 6 at once. Maybe they are mounted with the best electronics, that i capable of work until all 3 cells are really dead? I did not make notes from what laptop manufacturer each cell was.

PS. I also monitored DC IR of cells but haven't finished welding the pack yet. I'll test each bank (13P) of cells for:
1. IR,
2. capacity
3. 30 or 60 seconds 2C discharge (find and eliminate temperature hot spots by adding more nickel / copper)

 

[fesanand]

My experience is that in general Samsung is tops, LG second, Panasonic third, the newer Sanyos fourth and the Sonys and older Sanyos last. I can build an igloo with the number of dead Sony/red sanyo cells.

I agree with Samsungs being on the top.

Red Sanyo has many models, I've got really good results with red Sanyo with white-cap.
On the other hand, Red+green cap, Red+Red cap , Red + Blue cap have a terrible sag (even at 1C discharge) or they cut off before 1500mah. Not apt for ebike battery build.

 

[Hillhater]

Valuable information for builders using salvaged laptop cells.
..but remember, these are all old cells that have already had the best of their capacity burned up by being sat in a laptop for years. Most of them are down into the 80% remaining capacity range before the pack build.
Even when new, laptop cells are only spec 'd to operate a less than 1C Max, so in this "afterlife" use to expect anything near that is whishful thinking. The IR will be much increased and their deterioration will be accelerated.
Cell condition is likely more dependant on the quality of the charger and BMS systems in the original laptops, ..than anything to do with the cell brand or new cell quality.

, Red + Blue cap have a terrible sag (even at 1C discharge) or they cut off before 1500mah. Not apt for ebike battery build.

..a cell cutting off like that suggests it has a "protection" circuit in it...definitely A bad idea for a traction pack !

 

[dekes1]

Completely agree @hillhater - i dont expect Lipo levels of performance or LifePo4 levels of consistency. But for less than a quarter the price of a new Lipo bundle, the repurposed laptop cells are decent if you accept the limitations.

On a related note, now that i have a new iCharger 308Duo i ran a few quick tests (using the hacked hair dryer mod as a load) on my old pack to see how it holds up to massive draw. Here's my results:

14s10p pack made of primarily Samsung and LG cells of over 2100 measured mah:
Instantaneous Draw / Voltage / Calculated Sag/ Instantaneous Power
30 A / 51V / -5v / 1530W
50 A / 44V / -12v / 2200W
70 A / 33V / -22v / 2300W

I only ran the test for a few seconds because i didnt want to damage the cells, i was just curious as to peak momentary output