Battery won’t charge, but runs great

Esk8 Electronics
21

My concern is your lack of experience as much as the battery itself, given the timber suggestion.

I would measure the voltage of all the P groups. If they are still within 0.15 volts of each other, then I would assume that your battery can be saved. If the difference is more than that, then I don’t want to assume what might have happened to it.

You need a BMS to do the following things:

  1. Protect any P group from charging beyond about 4.2v
  2. Prevent any P group going below 2.8v (there could be some disagreements regarding this level, but anyway.
  3. Prevent the battery from charging above or below a temperature range. There is likely only one sensor, so temperate monitoring assumes a healthy battery.
  4. Provide short circuit protection to the output.

If you can understand all these aspects, you could replace the BMS, which is what I would do. A smart BMS with Bluetooth would be your best option, because you can then periodically inspect the voltages easily. If you have a group of cells that have an elevated self discharge rate - then that is a warning sign that a cell might be on its way to shorting, and if there are enough parallel cells, then there could be enough energy to start a chain of events leading the whole thing to go up in flames.

If you discard the battery, either hand it to a recycler for correct disposal, or ensure its discharged prior to putting it in the trash and risking the garbage collection truck catching on fire. I’ve heard Submerging in salt water will flatten any battery, don’t take the risk inside though.

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22

The cells in the possway are nowhere near good enough to ride consistently with no bms

You could get away with it on molicel for a while, but it’s a terrible idea for a small pack like that with lesser quality cells

Assuming this after known water damage and non-bms charge/discharge would be foolish

no no no no

discharging batteries is annoying but this is a horrible idea

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24

assumption is never good when it comes to battery and safety, especially when it is confirmed that battery compartment had water ingress

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27

I appreciate all the responses. I decided it would be safest to just dispose of. With that being said I planned to take it to a recycling center tomorrow as ours is only opened Tuesday through Saturday. I put it outside last night and it was still intact with no fire this morning, but when I got back from my classes it was gone. Assuming someone saw a big battery and figured it was worth money and took it…lol oh well I guess hopefully whoever took it doesn’t just toss it, but I have a feeling they will.

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28

its their problem now :rofl: at least u r safe

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29

Brian is right and you’re pushing reckless advice. Just stop.

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30

This battery talk clenched my asshole so much i think it tied itself in a knot, idk how im gonna shit now. Hopefully there are no more battery fires and pev regulations in our future :crossed_fingers: pray for the man taking a chopped battery off of someones dew-ee lawn :sweat_smile:

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32

Its been mentioned at least 3 times now that the battery was bulk charged AFTER it was suspected of being damaged.

This makes it impossible to know if any of the individual cells were drained below a safe level, and impossible to know if the battery can be presumed safe to use.

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34

Mate just because something is out of balance, is absolutely ZERO indication of whether or not it was under voltage before the bulk charge.

Balance isn’t the be all and end all of battery safety.

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36

Omg stfu

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39

Unless the person assessing has zero clue what they’re doing. You’re offering shitty advice based on a billion assumptions. Some of what you’re saying isn’t even true

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40

Just dumb. Whoever is erasing my posts is being silly.

It’s not rocket science figuring it out.

What assumptions? What am I saying that’s not true? There’s whole industries based on battery assessment

Telling people it’s too complicated to figure out and to throw it away… dumb

41

U are forgetting that the entire reason this thread was started was that it HAD A PROBLEM

op did stuff which MAY have made the problem worse

And you think that the battery is just fine

On top of that it’s a China pack with garbo cells

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42

I’m thinking no one knows. MAY is the key word. ASSESSMENT seems appropriate but instead, surprisingly for a diy forum, it’s said to be too complicated and told to throw it away

43

let me lay this out for u

  1. water ingress in battery compartment
  2. bms was fried upon checking
  3. pack was charged for at least 3hrs without protection

and u still think that the pack is still magically ok to use? u r just naive at this point

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44

This is in good faith, I’m trying to answer and not jump down your throat. I am being very direct and emphatic because this is dangerous, please understand that

This assumes that a damaged cell will always show a different voltage to its neighbours. This is not always true. Would it be higher or lower voltage? By how much? Why? There are many ways a cell can be damaged, even in just the narrow case of being shorted by water it could be shorted externally (water bridged the two terminals from the outside but never got into the cell), or shorted internally. If it’s external, that could be effectively the same as a piece of metal making contact and then getting blasted off, potentially burning the internals or not really doing much at all. If it’s internal, it could crystallise and make future shorts easier. Even if no short condition happened and water mixed with the electrolyte it will behave wildly differently. You cannot call a pack safe just by checking voltages and looking at it, but you can know for certain that it’s damaged if it doesn’t behave properly after exposure to water

This assumption is nonsense, you categorically can’t assume that.

Any useful information that could have been gleaned from measuring P group voltages is now gone, because as has been mentioned many times there was already an attempt at recharging it since then. Aside from the damage potentially caused by pushing current through a damaged pack, it can erase any signs that may have been there. If one group was shorted by the water-damaged BMS to 2V, it could now be reading 4V after a recharge. A damaged cell can still be charged, it doesn’t automatically drop to 0V to make it convenient for us to measure, it just can’t be charged safely or relied on any more

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46

The battery did not show problems. The bms showed problems. It’s an assumption the battery is damaged.

Is there no way to assess damage? There is

47

Neither of these are true though, and both are wild assumptions. Sure, charging doesn’t remove stains from water. But it can sure as hell bring voltages closer to each other and muddy the issue, especially when there are multiple cells in parallel

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48

Look, if the two are part of the same system and one is damaged then the system is damaged. The BMS is part of the battery pack, we’re not saying that definitely 100% the cells are damaged, but we know for sure the pack is in some capacity. If we know this, there is no safe way to assume the cells are good (edit for clarity: no safe way, by just measuring the voltages. You could validate it, but not in an unequipped home or dorm)

If I got in an accident and broke my wrist, it’s reasonable to ask if the rest of my arm got hurt too. You can’t surmise from the fact that there’s one obvious broken bone that that has to be the only damage and “we can assume it’s safe”. We know water got into the pack, we know it caused some damage, we know an attempt was made to charge the damaged pack, so there is absolutely no way to say we can assume the rest of the pack is fine

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50

When the stakes are “will I burn down my building and kill my neighbours” then whenever an obvious red flag comes up and there’s reasonable risk that the battery could be damaged, you have to assume it has been. And you said multiple times that if the voltage and visual inspection don’t look bad (never defining what good or bad means here), that you can assume it’s safe.

We can argue about what action to take, but no one with a clue what they’re talking about can argue that a basic voltage test qualifies the pack as “assumed safe” after it’s taken water damage

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