During the past couple of weeks I have been busy making a large battery bank using the eighty 32650 LiFePO4 cells I bought on eBay. The battery bank I am building is a 12V (13.2V nominal) 4S/20P one. With each cell rated at 5.5Ah the battery bank has a capacity of 110Ah, which is just under 1.5kWh.

While These cells are marked as 32700 they are technically still 32650 cells according to the datasheet, which is a little bit confusing. Since I am making a custom battery bank the actual cell dimension is not as critical.

For each paralleled group, there are twenty cells. I arranged them in 2 by 5 groups and paralleled each two groups of cells further together. In my opinion, this is a little easier to work with given the smaller size of each group. The cells within each group are welded together using 8mm nickel strips. If you are interested in making a spot welder yourself, you can check out my earlier post on how to make one.

Ideally, each cell should be separated using plastic cell spacers. Besides providing structural support, spacers also allow airflow among cells. This is helpful for heat dissipation and is crucial if Li-ion batteries are used, as thermal runaway can become a fire hazard. Li-ion batteries heat up when they are grossly over charged or discharged at higher than maximum specified current.

I used cardboard instead to group the batteries together since the batteries I used are LiFePO4 cells. This cell chemistry does not have the thermal runaway problem as Li-ion. As you will see later, the battery management system (BMS) I am using also limits the overall discharging current to around 100A. Since I have twenty cells in parallel, this overall current translates to just 5A per cell. At 1C discharge rate, the heat generated is negligible.

I did not take into account the possibility of individual cell failures within each paralleled group however. This could be a problem as some of my viewers had suggested. In this case, a bad cell could potentially damage its belonging group if not the entire battery bank. But for stationary use with a power inverter, this failure mode is highly unlikely.

Here is a video I made a couple of weeks (see below) ago on using the spot welder to make these 2×5 cell groups.

And here is a picture showing the eight 2×5 cell groups.

In the pictures below you can see what the final battery bank looks like after all the groups are wired together and the BMS added. As I mentioned in my previous post, I had to modify the BMS board so it can be used to balance the 110Ah battery bank.

I decided to solder these groups together using 8AWG copper wires instead of further welding them together. And for the positive and negative terminals, I soldered three 8AWG wires spaced across the entire length of the battery group to allow more even sharing of current. This is important as the maximum current through each terminal can be more than 100 A.

Here is a picture showing the BMS board, the negative battery terminal connector and the negative terminal used for charging.

Once I finished building the battery bank, I ran some load tests to ensure that the batteries and the BMS module are working properly. The video below shows me putting the battery bank through its paces.

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14 Thoughts on “Building a 12V 110Ah Battery Bank Using 80 32650 LiFePO4 Cells”

  • What are you using them for and how are they being charged? Are you using solar, wind, or some other renewable? I assume since you said that the battery pack would be stationary that you are using them in a home and not a vehicle of some sort? I am currently putting together a power pack myself but I am using lithium ion battery chemistry not LiPo like you used. I am hoping to be able to use it when going out to property that is not off grid, but the power can be very unreliable if and when there is bad weather during the winter. So it would be nice to have a back up other than a generator.

    • Hi Joshua, the battery bank is charged by a mains connected charger. I mainly use it to power my 1kW inverter in the event of a power failure.

  • I built a very similar unit with the same batteries. 4s12p. I am not able to keep them balanced. One 3.2v cell pack drains down to 1.8v while the other 3 cells remain at 3.2v. What could I be doing wrong? Can I post pictures here? How is your pack staying balanced?

  • Incidentally, this is the second pack I built. The first pack I built is a 4s4p 21Ah pack. It has the same problem whereby a single cell seems to completely drain while the other cells remain above 3.0 volts. I spot welded the small pack. This new larger pack (4s12p ~60aH) is being held together temporarily with neodymium magnets. I’m using .15mm thick pure nickel strip. It’s stationary and never moves around. I used those plastic battery holders for 32650 for stability. I wrapped the whole thing in Kapton tape. I built two of the large packs and put them in series for 24v. I’d really appreciate some help. I have a bms on the small pack, but the bms’s for the large packs won’t be in till mid April. I’m wondering if my configuration is incorrect or if the cells are just cheap and poor quality. Since you used the same batteries, I was hoping we could share experiences and I can correct whatever I have done wrong. Thank you very much.

  • I’m using a 4s 12v 100A balancing board which looks similar or is the same as you appear to be using. Mine is non-modified though.

    • Yeah, the non-modified version does not bleed enough current to be able to balance such large capacity battery bank. You will need to increase the balancing current.

  • I just purchased a 65A “Same Port” BMS off eBay. I’m hoping it will work. I’ll have to check out your video on increasing the balancing current of the ones I have. Thank you for your help.

  • Hello
    am Krish
    i have few doubts could someone pls help me out, actually i bought new 32650 lifepo4 batteries 3.2v 6aH, am building battery pack of 19S6P = 60.8V 36aH
    do i have to balance each battery individually(Charge, Discharging) or els can i building battery pack directly anyways am using 60V daly 20S BMS , pls don’t take me wrong am very ew to Ev filed and i want to build my own battery pack,Thanks in advance

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