Newly built 12s4p battery discharges in 1/8th mile

kchxaz · October 7, 2025, 6:37am

Having successfully built this same battery from Sony VTC6A cells a couple years ago, I know that the method with which I di this was sound. I am aware that all of the cells must be balanced top off, or whatever the correct word(s) are for it. When I bought the cells I bought like nearly 100 of them. 48 went into the first battery, the rest sat for a couple years (twice a year I charged them all to full with a little single cell charger I have). Very low amperage charger.

So before I built this current battery that is the subject of discussion, I once again charged each battery with the same charger. Over the course of the next thee or four months I slowly assembled and slowly completed the battery; lights, LLT bms (12s), attached brand new DV6 Pro VESC, it’s sweet. On my first ride I made it about 1.5 mile before the VESC suddenly died (I wasn’t watching my power levels, I expected to make it much, much further). Went home, charged it, used the LLT to monitor progress. Next ride I made it 1/8 mile, if that. Charged it for the third time.

Before going out again I thought I’d seek feedback. I know the 12 cell packs should all be within 0.10V of each other and that mine are .34V apart. I have tried leaving it on the charger and hoping the BMS would sort this out but the charger is a POS. It is either on or off, and it’s relatively high current - 3A. So once one, or more, of the packs reach high V limit, the charger stops.

Not sure what to try next. Disassemble the battery packs and cells and test each one? I’m not even sure what I’d be looking for. Nominal voltage? Peak? Anyone have any idea’s or suggestions?

chr1spe · October 7, 2025, 6:54am

Even 0.1 V, or 100 mV is a massive delta. I forget what the default is, but I have my packs set to 15 mV or 0.015 V delta at the top. There is a setting to have the pack continue balancing when not charging. I don’t use that version of the LLT app and actually mostly use the overkill solar app currently, so I’m not sure where it is on that one, but it should be somewhere. I would turn that on and set the delta to 0.05 V or 50 mV or lower. Someone else on here can probably tell you what is “standard”, but I prefer to have my pack very balanced at full charge and haven’t run in to problems with that.

As far as things cutting out, the first thing that needs to be known is if you’re using the BMS for discharge or not. If you’re not using the BMS for discharge and are just using the ESC cutoff, then either your setting for the cutoff is wrong, or the battery likely does have something very wrong with it. If you’re using the BMS for discharge, it could be many other things, but my money would be on the BMS throwing a fit about how unbalanced the battery is.

Edit: Also, don’t leave that balance while not charging on while the battery is unattended, especially since it seems the battery may be questionable.

tuckjohn · October 7, 2025, 6:56am

Something is seriously wrong with this pack.

What were the voltages of the cells after they sat for awhile (before you charged and assembled the pack)?

Have any photos of your battery assembly?

sevenfloorsdown · October 7, 2025, 9:21am

BenjaminF · October 7, 2025, 12:53pm

What cells is this pack made of?

kchxaz · October 8, 2025, 1:15pm

I do not recall. It was several months ago though. I did charge them to full before spot welding them together.

kchxaz · October 8, 2025, 1:16pm

Murata (formerly Sony) VTC 6A 21700 batteries. 4100mAh per cell. 48 total cells arranged in a 12s4p config.

hummieee · October 8, 2025, 2:38pm

See what the p-group voltages are with a multimeter when just cuts off and check temps then too. I think if ur not using the bms for discharge and it’s STILL stopping a group or two must be plummeting

SternWake · October 8, 2025, 3:18pm

Cells do not have such high self discharge that they need to be recharged twice a year, and they do not like being stored at full charge.

I had some Molicel P42A i measured when they arrived, and again before i made them into a pack 11 months later, and they were 3.47v on arrival and 3.46v 11 months later. They were stored in a garage in Florida over the summer, and the hot average temperatures would only accelerate self discharge rates.

So 5 year old cells stored at full charge are compromised to some unknown degree. Could this be why your pack is behaving as it is, can’t say for sure but is a strong possibility in my opinion.

It is also not the best idea to have them all at full charge for welding, as if something goes wrong and one ‘vents with flame’ it will have more energy and more flame to vent for longer and thus more time to catch the surrounding area on fire.

One other consideration is the charger you used to unnecessarily top them off twice a year. Some of these will overcharge slightly, so that if the consumer checks their voltage it is at least 4.2v, as in this day and age of the whiney consumer, if it only measures 4.16v after removal the average idiot consumer will throw a foot stomping tantrum, and give a bad review.

I find my Nitecore I4v2 charger will be applying over 4.2v at the end of the charge and the battery comes off at 4.209, and the cell is still 4.199v days after removal.

I try and pull them off before the charger quits on its own. If i forget or am not there, i will throw them in the flashlight and run it on turbo for a while and aim for 4.16v or less and close enough to full charge that i am not sacrificing any significant run time.

I got over ten years from the Panasonic NCR18650B before they started getting too hot for comfort when charging and I removed them from service, and drained them to 0.0x volts and recycled them

kchxaz · October 8, 2025, 3:58pm

Thank you for the feedback SternWake, and also information that I did not know before. That’s good advice.

If anyone has anything additional to add, I’m still listening.

kchxaz · October 8, 2025, 4:01pm

I did download the Solar kill app. Haven’t connected it yet. I will when I have plenty of time to mess with it

kchxaz · October 8, 2025, 4:06pm

Your comment reminds me…When I was out on my second ride on the battery (the last ride I took), I checked the battery via LLT app immediately after cut out. Much to my disbelief ALL of the p group cells were displaying exactly 0.1. Not 0.10 or 0.100 as the three decimals are in all other situations. Even more bizarre was that a minute or two after observing this, as I stood there watching, the p group cells all reverted to their true charges - just slightly below what they were when I started out. Totally flabbergasted, I just walked my board home a charged it to what you see above. Even though the charger does cut-out, I [try to] remove it as soon as I notice it stops.

chr1spe · October 8, 2025, 6:14pm

You still haven’t answered whether you’re using the BMS for discharge or not. That is a very important thing for people to know if they’re going to be able to help you at all.

hummieee · October 8, 2025, 7:15pm

I’m guessing u have a bad connection somewhere, maybe bad solder joint

kchxaz · October 11, 2025, 6:05pm

Sorry, I do remember you asking that question , but it was lost in my trying to remember all of them. I want to say no, I do not use the BMS for discharge, but I could be lying. The fact that the BMS tripped the over/under voltage tells me that it might be.

I did my best when performing VESC setup. I had major problems getting the remote to control the motors properly (connecting, correcting for rev/fwd - it seems switching any two of the three motor wires doesn’t work any more to correct direction). Verifying that the BMS is not controlling discharge is probably my next step.

And my charger sucks. It’s not down with balancing apparently. It’s either on and pushing 3A or it’s off, providing 0A. I have a DC power supply where you can dial in voltage or amps, maybe both, but it seems to me as you adjust one the other corrects for something. There is a switch that is either for controlling V or A but not both at the same time. Well, maybe to a limited degree but it’s tricky getting the voltage and amperage just where you want it. Especially as increased resolution makes it harder.

kchxaz · October 13, 2025, 6:14pm

So I’ve set the delta to 0.050A or 50mA, just to give it a larger target to hit. I see in this screenshot that the person supplying it has their “Balance only when charging” turned off. I did the same to mine. If that was not a good idea, could someone please say something and if you know why that’s not a good idea, could you please share? I’d like to know as well. There is obviously more to building a solid pack than just choosing quality cells, a decent BMS and strong soldering joints between connections.

Thinking back to when I originally charged the cells to full before assembly, I want to say I do remember there being some cells that were more charged in their topped off state than others. 4.2, 4.15, perhaps even as low as 4.0, but I specifically remember setting aside any that did not reach 4.0 minimum. I did not realize that the delta was so narrow. Figured it was just differences in cells as you might see in alkaline batteries. Until this post, I did not realize how critical it is to have not just the individual cells within a certain range, but also the parallel cells within that same delta. I did know that the overall battery needed to be balance, but this is where I thought the BMS came into play, eventually finding that sweet spot after some time on the charger.

That all said, should I be using a special type of charger that can adjust it’s current output? If a special type of charger is recommended, I am eager to hear what this is and why this would be different from a DC adjustable power supply. I have one of those and can dial in the voltage and current to the ideal charge specs, or rather, get them very, very close.

hummieee · October 13, 2025, 6:44pm

As long as it’s not pushing too much current for the cells it’s good.

SternWake · October 13, 2025, 11:44pm

You’ve been overwhelmingly vague on your build methods, and if you have been soldering directly onto cells, well there is NO battery manufacturer that says soldering to their cells is OK,…. that it just reduces longevity.

They all say “Do not Solder to cells.” and no established battery builder with any self respect will say soldering directly to cells is a perfectly acceptable build method.

There are not caveats like,” if you are skilled with a high power soldering iron with a large thermal mass, and work quickly, you’ll be just fine.”

No doubt you can find people that will say’ I soldered my battery pack and it has been going strong for X amount of time, performs better than new” and That their farts also smell like roses.

You wont find any of those people here. I don’t think there is any application more demanding of battery build method, or build quality than Esk8, and unsafe methods are called out.

Lithium battery fires are serious, very consequential, and law makers are dumbasses who love to revel in their ignorant self delusional authority to be the fuckwits they always assumed were the domain of their chosen villains.

They will enact stupid laws that Fuck over everybody, and there is obviously no shortage of easily manipulated fools who deepthroat, and mindlessly, but vociferously, regurgitate whatever they are told, as often as possible, as that is one of the few ways they can feel better about themselves, and their complete lack of common sense, and more importantly reinforce their perpetual victimhood.

I think your battery pack made from 5 year Old cells that were top charged twice a year with a single cell charger of dubious abilities, has much larger issues than just being out of balance.

If you really feel that balance is the cause of your 1/8th of a mile battery that you made, but do not know whether you bypassed the BMS for discharge or not when you built it, then you can try to set your power supply to 4.18 volts per Cell or so, and allow no more than 0.2 amps, and all 12 parallel groups of 4 cells should eventually all get to 4.18 given enough time.

if you still can only ride 1/8 of a mile then I’d discharge the pack fully, and recycle it.

if you have been soldering your parallel and series connections then I’d say don’t even bother putting it on a power supply at low amperage hoping the BMS is able to balance the pack, just get rid of the pack now, and be thankful nothing worse has yet happened.

Spot welders capable of welding 0.15mm pure nickel can be had for under 60$ now.

There is no excuse to solder series or parallel connections.

If you don’t know whether you BMS is bypassed for discharge or not, this raises a lot of red flags, as when building a battery one should basically be planning to bypass it, or not, and if it is designed to be used for discharge, it needs to be large enough to handle the maximum expected discharge, with a more than decent amperage overhead.