24V (10,5Ah) Li-Ion frog-style: 6S or 7S?

Dear Colleagues,

the frog-stlye battery pack of my mother-in-law`s ebike has a sticker Li-ion 24V / 10,5 Ah on it.

The battery is currently 1000 km away and I cannot open the battery pack to see inside. I could only get some pictures of the pack and I need to prepare in advance some replacement (maybe based on 18650 cells that are left over after building my own 14S6P). What is the exact number of the Li-Ion batteries in series that give 24 Volts?

6 x 3,6 = 21,6
6 x 4,2 = 25,2
7 x 3,6 = 25,2
7 x 4,2 = 29,4

I am quite skilled electrical engineer but here I am confused....

The second question is: I do not see any BMS in the battery box:


Am I just overlooking anything, is the BMS placed under the shrink tube or do they build the pack without any safety circuitry?

The last question:
The green battery pack`s size is about 13 cm x 6 cm x 14 cm. The single cell is then max. 13 cm x 6 cm x thickness. Can you advice me on any reasonable prismatic cell that I can use to build such a pack? (Aliexpress welcome)

Thanks a lot for your advice!
Nice regards
Karel

A 24V battery constructed wit lifpo4 would be 8s(X3.2v). Constructed with lico would be 7s(X3.7V or 3.6V). I have no idea what you have there.

marsalek said:

The second question is: I do not see any BMS in the battery box:

Am I just overlooking anything, is the BMS placed under the shrink tube or do they build the pack without any safety circuitry?

Click to expand...

Frequently inside the shrink wrap. That bulge on the end looks like it could a blank PCB (plane G10 fiberglass) used as insulation over the BMS.

Li-Ion
24v = 7s

10.5Ah = 5p?
measure the diameter and order shrink wrap to rewrap the battery,

then take a sharp knife scissor and open it carefully.

take the voltage of each cell
report back here and drink your fav adult beverage.

7P x 1.5 = 10.5 just another guess
It could even be LiPo envelopes rather than cylindrical cells.

I would suggest just build another 24 nominal volt pack (with new BMS) that fits in the same space.

Thank you for the constructive help. 7S is now clear to me. 5P with 18650s sounds reasonable. Based on my sketches/space calculations even 6P would fit inside, accounting for an extra 350g of weight.

We can close the topic