Comparing Making To Buying A Lithium Ion Battery Pack

At Hackaday we’re all about DIY. However, projects can have many components, and so there’s sometimes a choice between making something or buying it. In this case, [GreatScott!] wondered if it would be cheaper to make or buy a lithium-ion battery pack for his new eBike kit. To find out, he decided to make one.

After some calculations, he found he’d need thirteen 18650 cells in series but decided to double the capacity by connecting another thirteen in parallel. That gave him a 5 Ah capacity battery pack with a nominal voltage of 48.1 V and one capable of supplying a constant current of 40 A. Rather than connect them by soldering the nickel strips, he purchased a kWeld battery spot welder, adding to the cost of the build. He charged his new battery pack using his bench power supply but being concerned about uneven charging of the cells over the battery pack’s lifetime, he added a Battery Management System (BMS). The resulting battery pack powers his eBike motor just fine.

After adding up all the costs, he found it was only a tiny bit cheaper than prices for comparable battery packs on eBay, which were €24.4 per Ah (US$29.5 per Ah). The only way it would be cheaper is if he made multiple packs, spreading out the one-time cost of the battery spot welder. So that means it’s really up to your preference. See his video below to judge for yourself if you’d rather do it the DIY way. And then let us know what you’d do in the comments below.

If it’s the battery controller you’re interested in then check out this journey taken when a hacker ran into a controller which refused to charge its batteries.

 

29 thoughts on “Comparing Making To Buying A Lithium Ion Battery Pack

  1. It would be significantly cheaper with DIY spot welder, simple task at which [GreatScott] failed. [Ksayan TV] made at least three different spot welders from trash, Chcek out for example this one:

  2. To me it seems the biggest challenge is locating a source of quality cells (or a quality battery pack). There’s so much junk out there!

    I wonder if the Tesla megafactory is going to be flooding the market with cheap, high quality 18650 cells…

    1. The whole point of the battery cell megafactories is that tesla doesn’t have to wait in line like other companies depending on 18650 cells since they only prioritize themselves.

  3. There are definitely cheaper sources for materials like the cells and BMS. AliExpress has a few good stores for legitimate cells that are significantly cheaper. One can always go with a “weldless” battery assembly that uses mechanical pressure to hold the cells together. It doesn’t have to be this expensive.

  4. If you use recycled cells they are priced much better. I used the hover board battery packs ( bms included) for around $1.00 per cell. That allowed me to build a 24ah 36v battery for around $125. They all tested above 90% original capacity so the trade off is limited.

  5. I chose an Ego 56v (claimed) 7.5ah battery, this article didn’t mention final cost, but I think with charger I came in under $180.
    Also the Ego has the cells individually wrapped in a gel that changes state to keep them cool.

    If you advertise pack repair you can pay off the welder by fixing cordless tool packs. Many people have 2 or 3 dead packs, when only 1 or 2 cells are bad per pack.

    1. Kweld is sold out :(
      There are cheeay spot welders on ebay, but that Kweld looks good.

      Again a lot of facts missing from the article. And not even a link to kweld,

    2. I am a service agent for Ego – I LOVE when we see a mower etc come in saying it won’t charge. It in most cases just a few cells dead. I swap out the battery with a new one and take the dead ones home to dismantle and reuse. Probably got about 20 packs still on my dissassembly bench (each having 28 cells for the big ones). Most are The same Samsung INRs as shown that youtubers other videos about building his batteries.

  6. I would be interested in knowing the quality of cells in those eBay packs. Building your own pack gives you control over the cells you use, which would likely give you a much higher quality pack (if you use good cells) than you can buy on eBay. It surprises me that the cost was close including the spot welder, which means the DIY route could easily beat purchasing a pack (assuming you exclude your time).

    1. Definitely true. I feel like this guy is using all-premium components (for instance if I was building a bargain-basement cyberpunk ebike on the cheap, I’d just solder) and he’s comparing it to the cheapest available fleabay pack. Probably not quite the same value, but if you’re just looking to get it done without spending your own labor then that’s an option.

    2. His cost “calculation” is almost not present in the video.
      At around 10m20s he states very briefly that the cost of labour and the spotwelder was not included in his “calculation”.

  7. My trusty e-Bike needs a new pack soon as well. Current pack has around 10’000km on the clock now, and last winter it really started to show a lack of capacity, at least a lot more than in the last winter the year before (I ride the bike to work almost every day).
    A new original pack from Bosch (Power Pack Classic 400, 36V, 11Ah, 400Wh) costs around 400€ over here. So i guess, opening the old pack and just replace the cells inside could be considerably cheaper.

  8. Performing a single full charge/discharge on 18650s at <2C doesn't indicate their age, or ESR, or C rate. Discharging them at higher rates really tells you their quality.

    The eBay batteries I compared at 2C were either junk or comparatively more expensive than the HobbyKing solution. Even assuming my time and resources to build a 18650 pack were free.

    I just used two of these HobbyKing battery packs in the pouch. :
    https://hobbyking.com/en_us/multistar-high-capacity-6s-10000mah-multi-rotor-lipo-pack.html
    Got them when they dropped to $0.25 per Wh.
    Normally they're $71, ~$0.33 per Wh for a finished solution with no worry about mismatched cells or tearing the pack apart to fix them.

    My next project will use six 20Ah 3S (11.1V) pouches. During normal mode they'll be connected in two parallel banks with each bank having three in series (33.3V at 40Ah). This will give my 48V motor lower voltage for greater efficiency at cruising speeds. When I want a fast burst of power or higher top end, I can switch the battery configuration to be six pouches in series (66.6V at 20Ah). Total Wh stays the same 1,332Wh.

    https://cdn.shopify.com/s/files/1/2275/6915/products/dcb606-4_1024x1024.jpg?v=1510551473

  9. I’m just impressed that [GeatScott!] came in cheaper on a prototype inclusive of the cost of the spotwelder!
    What was the final range of the ebike using that pack?

    1. Once you’ve got the right tools , and the experience there’s often other uses you find.

      I’ve been considering an E conversion of my bike but the batterys have put me off but i might reconsider after seeing how easy it is to DIY

  10. I build my battery pack using recycled (full tested) 18650 battery too.
    But I’m surprised he can run his ebike with only 26 cells.
    Initially I used 13×5 cells (48v too), but BMS halted bike after few meters.
    So I used 13×10 cells and now run fine! It can ru about 40km with one charge.

  11. If you’re gonna weld tabs be sure to use PURE nickel strips and not nickel plated metal because the last would require a much longer welding time which decreases the batteries capacity

  12. If you live in a place like Hawaii there is often no choice but roll your own, as quite of lot of battery assemblies will not be shipped to the islands, but there are sources for single cells. Figuring in the cost of shipping @$10 per lbs air tilts the equation quite a bit in favor of DIY

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