Bottle battery cell count

[ChrisOfBristol]

I've been given an 18650 36V bottle battery by someone who no longer has the bike. I've taken the casing off to check it and was surprised to see that there appear to be two empty spaces for cells, so was concerned someone might have removed the cells leading to an unbalanced battery.*

There are three round layers, each of which has positions for 14 cells. The top layer only has 12 cells installed though, the bottom one has 14 and I can't see the middle layer. There are no signs that cells were ever welded to the links in the empty positions. The connection links are complex, there are links and wires and I can't see them all, so it would take hours to work out the connections and some of it would be guesswork.

I'm assuming that the middle layer has 14 cells, making 40 in total, and they are wired in 4 sets of 10. 10 in series would make 3.7 x 10 = 37V nominal - about right. If they were 2500mAh batteries, 4 sets in parallel would be 10000mAh or 10Ah - about right.

So it all adds up, it just seems a bit odd to make a battery holder with empty spaces. I suppose it might be the only practical combination in that shape. I'm inclined to assume the battery is OK, am I right to do so?


(*I'm checking it because it has a long history! I won't bore you with that unless you need some of these statements explaining.)

 

[E-HP]

I've been given an 18650 36V bottle battery by someone who no longer has the bike. I've taken the casing off to check it and was surprised to see that there appear to be two empty spaces for cells, so was concerned someone might have removed the cells leading to an unbalanced battery.*

There are three round layers, each of which has positions for 14 cells. The top layer only has 12 cells installed though, the bottom one has 14 and I can't see the middle layer. There are no signs that cells were ever welded to the links in the empty positions. The connection links are complex, there are links and wires and I can't see them all, so it would take hours to work out the connections and some of it would be guesswork.

I'm assuming that the middle layer has 14 cells, making 40 in total, and they are wired in 4 sets of 10. 10 in series would make 3.7 x 10 = 37V nominal - about right. If they were 2500mAh batteries, 4 sets in parallel would be 10000mAh or 10Ah - about right.

So it all adds up, it just seems a bit odd to make a battery holder with empty spaces. I suppose it might be the only practical combination in that shape. I'm inclined to assume the battery is OK, am I right to do so?


(*I'm checking it because it has a long history! I won't bore you with that unless you need some of these statements explaining.)

Cases support multiple configurations for different voltages. If you have a 36V pack, and the total number of cells is a multiple of 10, it's probably good (10S4P = 40 cells). The case could also support a 52V pack in a 14S3P configuration, which would be the 42 cells. You usually want to maximize the use of the space in the pack, but depending on the voltage may leave a few open spaces.

 

[ChrisOfBristol]

Sounds convincing, (and comprehensive) thanks!