Example of Ebike Battery Disassembly and Diagnosis

Example of Ebike Battery Disassembly and Diagnosis

In this video, Peter opens up a downtube battery pack that is unresponsive to try and identify the cause and find out of it is repairable.

In general, if there is no voltage on the output port of a battery pack, it means that either
1) The Battery Management System (BMS) circuitry has tripped for some reason
2) There is a break in the tab welds joining the cell groups together
3) There is a failure in the on/off switch wiring or fuse
4) The cells are fully discharged to an irrecoverable state (less than 1.5 V/cell)

Items 1-3 are usually repairable, but the only way to know for sure if a battery can be repaired is to open up the battery pack and measure individual cell voltages across the BMS header, which is what Peter demonstrates in this video. If all the cell groups are balanced and over 3V each, then the issue is typically from a BMS circuit that has tripped for irrational reasons and replacing the BMS (or sometimes just unplugging and reconnecting it) will restore to an operating state.

If you have one or more cell groups that is noticeably lower than all the other cell groups, then there is either a BMS circuit that is draining that cell (such as a blown bleed resistor mosfet), or there is a soft short circuit in one of the cells (rare with quality 18650’s), or you have a broken tab weld on one of the parallel batteries causing the group to have lower capacity than the rest.

If you have a case where the cells are all between 2V – 3V, then typically that means that the battery has been in stored in a flat state and the quiescent current draw of the BMS circuit has drained the cells below the shutdown cutoff voltage of the BMS. In this case, you can usually trickle charge the pack at a low rate (say a few hundred mA) bypassing the BMS until all the cells are over 3V each, and then after that you can reconnect the BMS and charge it normally through the battery’s charge port.

If you have any cell group that is less than 1.5V, then the only way to properly repair the battery is by replacing the cells, at which point it is almost always cheaper and much faster to just buy a new pack. Do not try to recover lithium cells that have been drained below to low voltages like this, it very often results in a massive inferno.

Readers Comments (34)

  1. Following !

  2. I think Jim Carey is your brother. Your the next future episode in Hollywood 馃槀馃槀

  3. Sharing Is caring December 27, 2020 @ 10:15 pm

    Do you fix dorado battery contact me on this fmehari290@gmail.com

  4. Qwe-esss-scent. Is how you pronounce it. Good video!

  5. Thanks. Get an ebay mic please/cheap.

  6. I see Hollywood in your future, Pete. Way to go! –聽 Mike

  7. Each of my cell packs had 3.6 volts per voltmeter readout but battery still wouldn’t run ebike. Could it be bad bms? Can those be purchased and replaced?

  8. The Jim Carrey of battery repair!

    Tip: if it had an USB port then most likely the 5V converter is what has caused the drain. Cells can last 2-3 years without voltage loss and BMS is seldom hungry enough to kill a battery in 6 months.

  9. I have a similar battery with on/off switch that won’t switch off what do you think the problem is

  10. excellent..!

  11. Many thanks for the video. How should one store batteries if not being used for few months. I read they should never be at full charge or extremely low charge. Batteries should be at about 40% and charged for about 30 minutes every month. Is this correct?
    I have just bought a spare battery from some who bought it new but never used it and this has been sat in his garage for six months. What is the best wsy to test it is working as it should? When battery is out of bike and power button is pressed for 5 seconds and released all five bars light up, indicating it is operating at 100%. It is the battery for Carrera crossfire. Thanks

  12. I’m wondering if you may know the answer to this question?… I have this exact battery and for some reason it makes a crackling noise when I switch the speed controller on? Any ideas?



  13. Yeah! More of these please! You folks are amazing in all aspects!

  14. Alright Jim Carrey good work. Show us bit of a surgery of that battery.馃槀馃ぃ

  15. So if i were to go travel for a long time, would the best idea be to actually disconnect the batteries from the bms to prevent this?

  16. Trickle charge the each cell with fully charge 18650 positive to positive and negative to negative for 40 sec soon they charge goes up to over 1v or 1.40 v then u bring them back to life then fully charge them I done it many times and it works…

  17. i have heard of people being able to recover 0 volt cells and getting back to working though it is risky and should be done carefully.

  18. David De La Torre December 27, 2020 @ 10:40 pm

    Jim Carrey electronic man

  19. Ebrahim Samsodien December 27, 2020 @ 10:41 pm

    Hi there how u doing is it worthied fixing my battery if there is some corrosion on the circuit board

  20. This is why some of us don’t like using a BMS in our batteries and would rather manage them ourselves. The average consumer want’s plug and play and that is understandable but it can cause early battery demise.

  21. Jim Carrey???

  22. Digiphex Electronics December 27, 2020 @ 10:46 pm

    You should do this with a bowl cut and blacked out tooth.

  23. thank you Grin!

  24. Urgent! Need instructions on disassembly of one sleeve bike battery. Case is all aluminium. About 390 x 110 mm

  25. Very great Video! very informative for many peoples that have broken battery!. One VERY IMPORTANT thing to also mention is that many chinese chargers wont take care of trickle current when connected to overdischarged battery and this might create alot of dangerous heat on the cells as their RI is higher than normal at this point. Many BMS wont have the UNDERCHARGING VOLTAGE protection feature which permanently disable charging to a overdischarged battery. Also overdischarged battery in very low range like below 2V, will suffer from copper migration from anode to cathode and will also have dendrite that grow perpendiculary from the electrode surface inside and over the time they become conductive!!.. these can eventually puncture the internal separator of the cell and make a direct short circuit! between anode and cathode… without any warn!… That is a serious information to know for people that want to use/recover overdischarged battery !

  26. Buy the self build E battery kit.$45 easier to replace a cell.and rebuild able.

  27. Hello sir, could we please converse with you about a battery exactly the same as the one you stripped down that isn鈥檛 charging. Do they have internal fuses?
    Thanks for taking the time to read this.

  28. roots No1 M Souljah December 27, 2020 @ 10:58 pm

    A paper weight…. A potentially very dangerous paper weight 馃挜

  29. Hi, i have a lithium battery problem in which my ebike dies whenever i throttle for too long or too much, then i have to reset my breaker to bring the power on again, can you tell me what the problem is? I hope you can help, thanks

  30. I thought you could bring them back as long as their was voltage. I brought some large format 64ah cells back from 1.2v and I only saw a small decrease in overall capacity(3 or 4ah). I haven’t seen any internal discharge. I left them at 2.8 for a month to see if there was any decrease in voltage( no change over the month).

  31. My battery showed 84% life today before it shut down. I may have asked too much of it while trying to plow through some deep snow.
    Input (where it’s charged) shows 29v and output (where it connects to the bike) is giving 3v.
    Is there a way to reset the BMS?

    Turn Life 48v/14AH 672WH


  33. That’s cool, the guy looks like and got the same expressions as Jim Carrey!

  34. What a bad bms . That鈥檚 way I build my batteries my self . Imagine buy a good battery with Panasonic cells and a 5 dollar bms ruining the pack . This is not acceptable. I failed finding a good bms to buy for my ebike and I come with idea to use a Hilti 36v battery bms . Gues what? Works flawlessly.

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