Inside a 30K Li-ion Battery Pack

So I opened my 15-month old 24V 10Ah Lithium-ion battery pack from LEED (e-bikerig.com). Here is what's inside!

1. LSW153-45-6 controller
2. Cream-colored plastic enclosure wrapped in black rubber heat barrier
3. A 7S4P (7 series 4 parallel connected) 28 pcs. of Samsung ICR18650-26F 2600 mAh cells wrapped in black plastic shrink wrap
4. Battery Management System (BMS)* attached to battery cell pack

*The BMS controls the input-output to ensure that each cell gets enough charge and are all balanced. When one cell gets below the charge threshold it shuts down the pack. No output. When charging, once each cell reaches its full charge, either the BMS, or more likely the smart charger sold separately, shuts off the charging.

Why I opened it? The pack failed after 1.3 years of ownership

This old battery pack was delivered to me back in January 23, 2014. I paid 314 USD for the battery and shipping costs to Norway. I paid an extra 46 USD for custom duties. All in all it cost me 360 USD.

On April 23, 2014 (3 months later), the battery pack stopped working after a long uphill climb of about 1 km. The two kits I have been using tend to die out in long climbs so I had to be cautious the next time I used them. However, since this 30k pack stopped working, I sent it back to LEED on June 20, 2014 (about 2 months later). The battery is still under warranty.

However, it took about 4 months before I got the replacement since the retailer had to send the defective battery back to the supplier in China which sent a replacement to my retailer, then to me. So I got the replacement October 8, 2014 and started using it October 16, 2014. I used the battery pack from then on until it stopped working on January 16, 2016 (1 year and 3 months). Not bad for a 360 USD battery pack that lasted 15 months (3 months beyond its 1 year warranty). Note, however, that I did not use the pack everyday so I am sure I have not LITERALLY used it for 1 year. I am also certain that I did not charge it more than 600 times nor more than 1,500 times.

My 30K battery lasted about 100 charge cycles only

The 30K battery itself is advertised as good for 600 charge cycles at 100% capacity. But since I only charged it for a maximum of 100 times (I log my charges) the advertised maximum life in terms of life cycles has not yet been fully exhausted, only the maximum time of ownership guaranteed has passed.

Does anyone use and charge their battery 2 times a day for 300 days in a year? 

Unless the battery pack is used 2 times a day and charged 2 times for 300 days, the 600 charge cycles at 100% capacity advertised specification will not be used up during the 1 year warranty period.

To actually use up the 600 cycles and 1,500 cycles in a more realistic sense, 1 year and 8 months is needed which is equivalent to 600 days of daily charging. Therefore, to really guarantee the 600 cycles, the warranty should be at least 20 months, since 1 year is too short to test it.

Use your battery 2 times a day for 365 days to maximize warranty

Only if the battery is used 2 times a day for 365 days can the 600 charge cycles advertised be used up. Even if that can be done (which I was not able to do), that is only 730 charge cycles for the whole 365-day year. If that is done, only use 600 charge cycles at 100% capacity can be used plus 130 charge cycles at 80% capacity. Given that, the battery pack is supposed to have 770 charge cycles left at 80%.

Are there any users out there who have actually used their battery beyond 600 charge cycles (i.e. 20 months of daily charging)? Let me know if there are any.

BMS shutting down discharge due to failing cells

I suspected that it is either the controller that is busted or probably the Battery Management System (BMS). Using a multitester revealed that the battery is still charged (the charger indicates it is) but I do not know why the pack stops discharging when I connect it to the motor or my inverter. My new battery pack powered my inverter just fine.

The BMS seems to be shutting down the output from the pack (probably because one of the cells is below the charge threshold or is failing). According batteryuniversity.com repair is possible. You just need to replace the failing cells if the other cells are still good. I have not done that for now because I do not have the equipment and the know-how yet. Maybe in a later project I will try doing this. In the meantime, I have one controller to spare in case the controller of my other battery pack breaks down. I also have some spare cells to use (if they still work).

Opening the pack

Here is how I opened the battery pack.

I removed the black plastic wrap using a cutter, detached the controller, removed the 4 screws from the plastic case, removed the black plastic wrap from the battery cells and pulled out the cells attached to the BMS. I did it carefully to avoid short-circuiting the Li-ion cells.

I used a multitester to see if the battery is still charged.

The tester is set to 250V, hence the low meter which is about 26V. But later testings show that the charge is falling rapidly from 10v down to 5v etc.

So aside from the controller module outside the black rubber wrapped cream plastic casing, there is a BMS attached to the side of 28 bundled Samsung cells.

The cells are labelled ICR18650-26F (SAMSUNG SDI 2E54). It is 2600mAh 3.7 volts each. Amazon sells these 18650 cells for 5.18 USD each (so 145 USD just for the 28 cells). LEED sells the pack for 349 USD. So the mark-up and the plastic casing, wiring, connectors, and the BMS probably costs about 155 USD since the controller costs 49 USD.




Here are the components of the attached BMS:




Here is the schematic diagram of the wires connecting the pack and the BMS:



The chips on the BMS board include the following:

C404BA 525



P75NF75& CZONG 5 MAR 308



Several of these smaller components: 331, 102, 305, 0, 105, 089, 103, 101, and RD10.

What is inside other battery packs?

I wonder what is inside other packs? If you have tried opening your own pack, please share. For example, I am interested in seeing what is inside Clean Republic and ALLCELL packs.

NOTE: More posts on e-bike conversion projects are available here.