I have lots of old laptop batteries due to retiring laptops, capacity problems ('doesn't hold a charge'), or pack errors, and have been slacking on recycling them for years. Most of these were from Lenovo and Dell machines, but I had a few oddballs (Toshiba, Compaq, etc...). So I decided to take them all apart. Most laptops made before a few years ago are made of '18650' cells, which look like large AA batteries. Each of these cells has a nominal voltage of 3.7V and typical capacities of 1500-3000mAh. Most modern cells are approaching 4000mAh capacities with some 'high capacity' cells being advertised at nearly 10000mAh, but you don't have any of those in the old battery packs you have laying around. Most modern 'thin' laptops have moved away from 18650 cells and are using plate-style batteries for packaging reasons (thickness, odd shapes, etc...).
You've probably head the '6-cell standard capacity, 9-cell high capacity' terms before. This is referring to how many 18650 cells were contained in the packs. These packs are typically rated somewhere in the 10.8-11.1V range with a pack capacity of 7-8 Ah. The voltage rating is a little vague as the cell voltage actually ranges from ~3.1V fully discharged to ~4.2V fully charged. Those cutoff voltages vary between manufacturers and model lines. With 3x 3.7V cells in series, you make an 11.1V pack. If you make that up of 2600mAh cells and tie 3 of those packs in parallel, your 11.1V 9-cell pack is 7800mAh capacity. On paper.
I bought a fancy charger/tester which works with these cells. But also other size cells and other chemistry batteries. So fancy.
What have I found so far? I've recovered 63 cells from ~9 battery packs with either 6 or 9 cells in them. It appears I have 6 different cells across all these packs with capacity ratings from 1600mAh-2800mAh:
9x Yiklik (Chinese cells?)
36x Sanyo (3 different cell types)
I've charged and tested 35 of these cells so far and have found the following:
17x dead cells (no voltage/continuity)
6x substantially reduced capacity cells
10x cells at or above 90%
The Yiklik cells show an interesting picture (from a Lenovo battery IIRC):
These cells are rated at 2100mAh. 6 of the 9 are at 90% while the other 3 are < 20%. This battery was in the 'reduced charge life' pile, but 2/3 of the cells are still perfectly functional from a capacity standpoint.
Other remaining tests:
- Internal resistance - usually correlates to how hot the battery will get during charge/discharge. Too hot = melting and/or fire
- Self-discharge rate - how fast does the cell dissipate charge if left alone? Manufacturers usually rate this in the low-single-digit % per month. This only matters if your cells go long times between usage.
The 'dead' cells are that way for usually for one of two reasons:
- Chemistry is dead
- Internal cell protection circuit tripped
The latter is due to a number of possibilities, one of which is extreme discharge. You can 'un-trip' this circuity by running 4-5V across the cell for a few minutes to reset it. I may try this on some of the cells, but likely won't have much success. The 6/9 of the Sony cells are this way but the 3 that aren't have < 11% capacity remaining.
For reduced capacity cells, they can sometimes be partially restored by running a number of charge/discharge cycles on the cell. The charger has a mode to support this, but the manual warns this can take '10s of hours' to run.
Then what? Some people are harvesting cells to make 'Tesla Power Walls', others are powering electric bikes/go-karts/cars with them. Other people are doing interesting things like replacing the the sealed lead-acid batteries in their UPSs with Lithium packs. What am I going to do? Maybe the latter. Maybe nothing. If it's something, I'll need to invest in pack construction materials and battery management systems to keep the pack safe while charging/discharging them.
What is the economic argument for recovering cells? Cost. New cell prices vary widely in the $4-10 range depending on capacity and charge/discharge performance. If you can recover cells at a substantial discount, that can offset the typically lower capacity of recovered cells you receive compared to their newer equivalents. Ebay is full of used laptop battery 'lots', but the pricing doesn't always make sense and can sometimes cost more money per cell than new when you factor in shipping and dead cells.
What does the future look like for this practice? Bleak, I think. As modern laptops shift to 'plate' batteries, the used market for 18650 cells will dry up. Also China is starting to manufacturer high quality high capacity cells and is selling them substantially cheaper than the manufacturers you've all heard of (LG, Panasonic, etc..). I've seen some quantity buy/sale pricing approaching $1/cell for new cells, which is about the equivalent pricing for used cells when you factor in shipping and losses.
Should you all give me your 'old' laptop batteries? I have a hard time turning down free stuff...
Don't lose those screws...
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