18650 Cell Stuff - 0V cell? - Page 1
Forum section: electronics / projects

author: paul_g_787
author_rank: Frequent Contributor
timestamp: August 13, 2023, 01:52:48 pm
content: Further to my recent post of my laptop battery replacement I have delved into the world of re-using the cells. I intend to put them into some of those empty USB power banks to use while camping.My original Lenovo battery there are 8 cells. 2 strings of 4 series cells - 1 string of 4 small square cells. (Not pouch cells though but square rolled cells) and 1 string of 4 18650 cells.The way this battery worked was it would drain the 4 square cells first then when they ran out would switch to the 4 18650s and drain them. (I am told this is a peculiar design).Unfortunately the BMS board has died and one of the chips appears to have let the magic smoke out so I scrapped this battery and ordered a replacement.I removed all 8 cells and they have all charged up individually using a a single cell USB BMS board from Ali express. I notice that after sitting for 8 weeks the 18650 cells still have over 4.0, 4.1V but the square cells are all 3.75V , 3.8V.I ordered an Ayree brand battery from amazon as a replacement which arrived dead with 0V output. After complaining they sent me a new one which is working great and I have been using for a few months.I opened up the faulty Ayree battery to find a 4-cell BMS. and the cells are connected in 4 parallel pairs. One 18650 paired with a square cell. Then these four pairs in series.One of the pairs was dead at zero volts. I have separated these 2 cells and the square cell is charging up OK so far using the single cell USB BMS board. However the 18650 charges from 0V to 0.2, 0.3V then starts to drop in voltage slowly. I am wondering if this cell is dead? My guess is this cell has died and discharged the square cell in parallel. I presume the BMS turned off due to the cells being sub 3.5V for some time?The square cell is comping up at 4.1V currently and is not excessively warm considering it has been charged from dead dead flat. It is at about 32 degrees C in a 22 degree room.The other cells are all between 3.1 - 3.5V and I am going to charge them up one at a time and see what happens.As for the 18650 that is dead is there anything I can do to try to wake it up? Obviously so it is safe to use of course.I am going to capacity test these cells once I have determined the useable ones.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 13, 2023, 03:15:02 pm
content: That cell is bad, only thing it's good for is recycling.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: August 13, 2023, 03:24:58 pm
content: Quote from: NiHaoMike on August 13, 2023, 03:15:02 pmBut what would cause a brand new cell to measure 0V? It's manufacture date is less than a year old so I would have thought it unlikely (although not impossible) for the cell to be bad seeing as my used cells from my original 2010 battery are all coming up ok.I am guessing what might have happened is that something, maybe in the BMS circuit had a short across that pair of cells and discharged those 2 cells down to nothing, the other one that was in parallel has charged up just fine though so shy does this one in particular not charge?It sits at 0.2V for ages.

author: amyk
author_rank: Super Contributor
timestamp: August 14, 2023, 03:55:10 am
content: If it won't hold or accept a charge, it probably has a partial internal short. My guess as to why is a manufacturing defect. While taking suitable fire precautions, if 100mA for a while doesn't cause the voltage to rise, and it immediately drops back down to 0 quickly once disconnected, that's likely what happened.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 14, 2023, 04:40:45 am
content: Unless I missed something in your posts, a well-behaved BMS will actually cut off the output below the rated cut-off voltage of the cell. Often around 2.9V. So a deeply discharged battery can measure near 0V. Doesn't mean the cell itself is actually sitting at 0V. So, again unless I missed something, like if you have measured the cell voltage directly.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: August 28, 2023, 08:03:44 pm
content: Quote from: amyk on August 14, 2023, 03:55:10 amYes tried that approach after your suggestion. Immediately back to 0V again so I have disposed of this cell now. Shame it went faulty.The cell that was in parallel with it appears to have come back to life with minimal problems after 3 charge and discharge cycles at about 1890mAh (it is a 2Ah cell).

author: paul_g_787
author_rank: Frequent Contributor
timestamp: August 28, 2023, 08:10:50 pm
content: Quote from: SiliconWizard on August 14, 2023, 04:40:45 amYes the BMS of the laptop battery the cell came from did exactly that and so do my cheap Ali Express single cell BMS boards I have used to charge up these cells.I was measuring the cell directly after it was removed from the battery pack. Unfortunately it is dead.One salvaged cell is from a free USB battery bank I was given at work. it is 2.2Ah and has 2150mAH of capacity.The 3 remaining 18650 cells from the new but faulty laptop battery are rated 2Ah and have capacities from 1891mAh to 1992mAhThe 4 18650s that are 12 years old from my original laptop battery are between 399mAh and 1828mAh. A few are a bit low but work for now.I have installed these 8 cells in a USB emergency bank and I am getting 10.1Ah from them in totalNot their full capacity but at least I am re-using them for a practical purpose instead of binning them.I get to charge my USB bank on the train and at work, then charge my phone for free at night now using only a £3.90 battery bank and free used cells.Will try and salvage more cells to replace the crappy ones down the line.Might even make another bank with the 8 square shaped cells I have.