Harvest 18650 cells from discarded laptop battery – salvaging a discarded power bank

• I had recently procured an 11000 ma power bank from Amazon.co.in. It turned out be incapable of holding charge beyond 10 minutes !

• I sought replacement. Perhaps the vendor did not have any and instead offeredme full refund. I was now saddled with a power bank with seemingly good electronics but nearly dead batteries.

• I decided to try out some experimenting with discarded laptop battery with a view to see if I can salvage the power bank.

Opened the power bank and found 4 in no 18650 Li-ion batteries in parallel. Though the power bank seller advertised and sold the power bank as 11000 mAh. However with 2000mAh as average cell capacity, the power bank could not have been more than ~ 8000 mAh capacity. Lesson : power bank sellers quote any marketable mAh and unless one opens the power bank , the ambiguity remains.

Disconnected all 4 cells in parallel and measured individual cell voltage using multi-meter. Only one cell showed some life i.e. showed terminal voltage ~ 3.5V rest 3 were nearly dead with terminal voltage under 0.5 V. These were marked for removal.

Careful , the dismantling exercise can cut/bruise fingers.

Decided to try out an old laptop battery. Purchased one discarded laptop battery from lamington road (Mumbai) for INR 100 (approx $1.5). Ripped it open and found inside 6 cells in series + parallel combination with associated charging electronics and battery temperature measurement thermisters on battery surface. Dismantled the contraption and isolated each individual cell. Cleaned the surface & cell end terminals. Measured voltage of each and found all cells in the range of 0.4 to 1.6V. Since I already had once cell measuring 3.5V, I picked 3 best cells (though these measured around 1.6 V).

Careful , the dismantling exercise can cut/bruise fingers.

Replaced the defective cells with 3 best cells picked from discarded laptop battery and made a temporary contraption to see if these semi-dead cells could be charged and put to good use.

ImportantCheck battery polarity. The slightly protruding terminal also marked with a circular grove is cell’s (+) terminal. The opposite side i.e. flat surface is the (-) terminal.Check series / parallel connections to power bank circuit is correctly complied with

• A lithium ion/polymer cell is nominally 3.7V or so but the voltage needed to fully charge it is more like 4.2V and the voltage when fully discharged may be more like 3V. Internet gyan suggested that I discard cells measuring under 3 V, however I found that the cells that measured ~1.6 V came to life after being subjected to over 24 hrs charge cycle. These cells now showed terminal voltage of ~ 4.2V

• Note : Most batteries are considered over-discharged or dead when their cell voltage is < 2.8 V, but even in this situation, cells can be charged again and be reused. Give it a try prior concluding anything.

Note :

Soldering of old cells can get tricky and the key to successfully solder & make a good joint is to properly clean the surface , scrape the surface with something sharp and use flux to solder.

Conclusion : I now have a fully functional power bank and I have tested it with my Android mobile. This power bank does give me 2 full recharge and yet has little juice left! Note: One doesn’t necessarily have to buy a cheap power bank (but with good electronics) . Amazon / e-bay sell DIY power bank case with electronics for ~ INR 350. Put in another INR 100 odd for an old discarded laptop battery, you have a worthwhile week end experiment at hand!