Backyard Aquaponics
A place to discuss aquaponics

I understand that I shouldn't use a soldering iron on my battery packs but have no idea why.

What is the danger, to me or the chance of damage to the batteries. ie why cant I solder them?

What sort of batteries?

Makes sense for button batteries, due to heating them up too much. You might get an explosion if you try hard enough

No issue for batteries with a soldering tab!

18650 Li-ion without tab, button + ends or anything that looks like the ones with the charge controller bit at the end.. (it doesn't say Li-ion anywhere on the battery but I presume they are)

I think (but I'm not sure) I've isolated the bad ones, and I'm aiming to buy some to replace the faulty ones. This brings me to my other problem, and that's mixing clusters of different capacity (same voltage). I have no idea if that's a problem.

It's an old ebike battery with 40 cells arranged in what looks like groups of 8, connected into 5 clusters. That doesn't quite make sense though because It's supposed to be 37v, and the cells all seem to range from 3.6 to 4.1 volts except for the one column that reads less than 1v.
On the other side of the batteries there is less obvious connections which no doubt explain how they get the voltage to 37v.

I'm getting more confused by the minute





The fourth column from the left on the last photo reads 0.91v when I test across any cell in that column. The rest all show 3.6v to 4.1v .

My plan is to pull those 4 batteries out, test them (partly to find out what they are), then replace any faulty ones.

If I buy batteries with soldering tabs, can I solder tab to tab, or am I still soldering the other end of the tab to the next battery?

This is written on the side of one of the cells, but none of the numbers bring up anything in a google search, except a company name (Hengdian Group DMEGC Magnetics Co.,Ltd) and battery size (18650).

Buy batteries with tabs and solder the tabs to tabs or the existing "bars".

I think the issue of soldering to the battery is it damages the battery or the electronics inside it for the protection circuit.

3.65V is a common charge voltage for LiFePO4 chemistry, but there is no guarantee that's what it means, maybe it is the operating voltage at a certain rate of discharge of a different chemistry battery ... impossible to say.
As long as the capacity is similar it shouldn't be too big an issue, but bad cells in parallel with new will reduce the life of the new ones, as they will be worked harder. Bad cells in series with new will kill the bad ones quickly as they go down to <1V and cant be recovered, but can explode when charged.

Cool. OK thanks.

I think the red wires might be to detect the charge of each cell. I think there is something that does some balance thing or sommit. There's a board on the battery pack with a dozen or so red wires coming from each cluster of cells.

Hopefully that means that only one cluster is fried.

Even more hopefully, it might mean only one battery is fried.

I have a lot of hope.

This thing is going to be a sonar switched, weed-wacker, bird detector that casts an umbrella of hope over my fish when it detects a cat feast in progress.

No cats or birds will be injured... just hopefully freaked out.

Alternatively I might just use it to squirt a water gun at them.

OK tab to tab. Cool

That means I should be able to repair my existing links. I will have to cut the thing to bits to test each battery... at least within the cluster that shows under 1v, so if I buy some of the tab ribbon stuff I can make bridges to existing (cut) tabs, and buy new cells with tabs to join.

Does anyone else think this is going to be very messy

Shopping list...

Tab ribbon stuff.
Full body fireproof suit.
More household fire extinguishers (Why does everything I do make fire except when I try to make fire?)
Some batteries of unknown chemistry.
Some kind of education beyond year 9.
Extra luck.


I think that's everything.

I found the ebay purchase (Mrs Bullwinkle's account) and it says this...


"For Electric City Bike Bicycle e-Scooter EBIKE 36v 10AH amp lithium Ion BATTERY"


So I'll just go with it, and charge it outside on the driveway the first few times to see what I get.

Can you make any sense of the wiring of the clusters of cells?

I thought they would be just wired up so that there were groups of batteries that made up 36v. But each cluster is connected to the next, and then there is the odd column at each end of just four batteries rather than the eight seen throughout the rest of the pack.

Am I correct in thinking the error lies within that 4th column?

Feel free to just walk away from this chaos (sorry to bother you).

very funny. Good luck.

From the photos is is not possible to figure out the wiring. You need to draw it all up on a sheet of paper to figure out where the series and parallel connections are.

Ok thanks. I'll give it a go.