The battery builders club

I dont own a fast charger - i think it takes 3-4 hours for a full charge with the charger that I have. Do you think that is slow enough?

There’s no real threshold for fast/slow. The slower you go the better since that makes the balancing current a larger percentage of the total charging current and that allows for more balancing to be done before the pack is fully charged.

Charge with whatever you have and, if you can, set your BMS to balance when not charging. You might find it all balances out after a few of days of sitting after this charge or, depending on how the BMS wants to work, you might have to cycle the pack a few times in order to get it balanced.

Another option, to check the health of the pack, is to charge it fully and let the BMS try to balance the pack. Once the BMS seems to have stopped doing that then turn off balancing and leave the pack alone for two hours or so for the voltages to settle.

Then measure each cell voltage and then leave the pack alone for a week or longer. Then check each cell voltage again. If group 11 is a lot lower than the other groups then you either have one or more cells that are damaged, have reached the end of their life, or something is wrong with the pack or the BMS.

If all the p-groups look fairly close together in voltage after a week then your pack might be okay to use.


Hey, you’re private so i cant dm but maybe i can help. Im in the pmw usa (Seattle specifically) and id be willing to take a look at it for you and get it balanced and run a few charge discharge cycles if youre interested. Im not fast, it’s just a hobby for me, but i have all the equipment.

I also collect used cells for a power wall and recycle packs for various uses but if im testing it for you i dont buy them, to conflicting interest for me. Either i buy it or i test it.

Imho that pack will probably come back into balance but idk without putting it on my bench


$3.99/cell for Samsung 40T 21700! (33% off) Are there any other cells this affordable these days? How often do you see sales like these?

Thanks for the advice. I am using the Apex Smart BMS and app im using it with is the Xiaoxiang BMS, whcih apparently contains: “Balance wiring harness…”. I cant see anything specific in teh app that says ‘set to balance’, or anything similar sounding, are you famililar with this app by any chance?

EDIT: Jusrt seen this option here, guessing I need to set the balance mode to static to follow your suggestions?

(also, how do the other settings look? - ive never played with this, just used it as I received it from the battery builder)

I apprecaite the offer of help, but im in the UK, so am going to go with Mooch’s advice and charge it and try and set it to balance in the BMS and just leave it. Btw, is there anything in my BMS settings that need tweaking? (I posted them above).


Looks good to me, the current used to balance is usually very small so be prepared to watch it for a few days. Im not familiar with the spec on that bms so I don’t know if it has active balancing or resistive balancing, maybe someone with direct experience can chime in. If it is resistive the bms may need to discharge all high cells in order to bring the low group up so it may get warm… but never hot. Remember to charge it in a fire safe, and preferably environmentally controlled place. And don’t leave it unattended, only charge it when your home, safety safety bla bla bla. Good luck, hope it recovers for you

1 Like

I got P42As from them for $4.50 a cell a couple of months ago. I prefer that deal. You usually have to buy pretty big bulk to get close to that deal though. I don’t have the experience to know how true it is, but people around here seem to think Samsungs start having issues pretty quickly sometimes.


Sorry, I’m not.

1 Like

Thanks man, i appreciate all the info here :+1:

1 Like

Regarding cutting your own nickel. I bought a 30mm x 0.2mm roll which covers the tops of a double stack, but I then need another piece attached for the bend tab. Do i then weld another piece of nickel on to make the tab? What joule setting is required for this since it would be 2 pieces of 0.2mm nickel welded together? Is this how this is supposed to be done.

I couldn’t find any 50mm wide so I could just have 1 solid piece of nickel instead of doing this.

Every welding setup is different, but generally nickel-to-nickel takes more beans than nickel to cells (cell cans are steel). You should experiment till you get good strong results.

1 Like

cant find any images or videos about this to use as a visual aid. How many total welds to secure the 2 nickel together?

im basically trying to mimic something like this

The general rule of thumb used around here is that each weld is good for ~5 amps, so the usual six welds (three pairs) per cell connection is good for ~30A. It should be pretty safe to extrapolate that out to the full pack design current.

1 Like

Thanks to knowledge gleaned from you fools, I swapped sunpow 21700s in a dead Amazon pack for molicel 42a (6sp1, bms in pack.)

I have a second pack (pictured above) I might put some more in for another dyson.

This thing sucks now. Thanks a lot.


When you’re too lazy to get out of bed to clean your apartment


This might interest you:


gawd damn



Haha yeah that had me rolling too


Hee, In trying to charge my battery pack, but it doesn’t charge to 42V (10S). It stops around 40V and the charger will go green-red-green-red as you can see in the video. What should I do?

1 Like