Battery does not charge above 10% all of a sudden

[Cyclomania]

So I have been using this 48volt 18ah battery for quite some time now. But it has not shown any signs of diminishing amp hours or anything like that. Not anything that I have noticed.

But today the bike just stopped all of a sudden. And the battery was showing like 5 max 10% charge. I had to walk it home from there.

Well at home I tried to charge it. And I know the charger is not the problem because I have charged other batteries with it today.

I have tried both the regular hole for charging and going trough the xt60-connector as well, with one of those adapters to see if the hole could be the problem. But when trying to charge it through both of those ports the outcome is the same. The charger is showing the green light, for fully charged battery. I have no idea why. Because when I test it with a multimeter it is charged only up to about 40 volts right now. And this is a 48-volt battery.

Also, when having the charger connected to a wall and the battery connected to the bike, the bike will start. Because it seems the charger can then run current into the bike via the wall.

Any idea what has happened here? The cells just went caput and on strike one day and decided to not be charged anymore? Or am I missing something?

If the battery life is going down I thought it would be a more gradual decay? For example maybe one day it would only charge up to 80% or so? But not like this to just not charge anymore one day. Not above 5-10% at least it seems. At 40 volts the charger is showing the green light for fully charged when connected to this battery.

Maybe I rode the battery too close to being completely emptied one day or something? Anyoe has an idea?

 

[E-HP]

So I have been using this 48volt 18ah battery for quite some time now. But it has not shown any signs of diminishing amp hours or anything like that. Not anything that I have noticed.

But today the bike just stopped all of a sudden. And the battery was showing like 5 max 10% charge. I had to walk it home from there.

When you say stopped all of a sudden, under what conditions? Riding normal speed on flat ground, riding fast, climbing a hill, etc.? My guess is the BMS tripped and isn’t resetting, possibly due to some weak cell groups, and the 40v measurement is some residual charge from the caps or something, but hearing more about the symptoms may shed more light.
What is your normal charging routine (charge when empty, charge at 20%, etc.)?

 

[Chalo]

Inspect all the plugs and terminals in your charge and discharge wiring. If one of them got crusty, it will manifest as a large voltage drop that gets worse as more load is applied.

If that's not it, then likely you have a cell voltage problem in that pack that's causing the BMS to reject charge, cut off discharge, or perhaps both. That's the next most likely thing. Then there's the smaller possibility that the BMS is faulty and is cutting things off without cells going out of bounds. It happens occasionally, especially if the pack has been short circuited at any point, but it's a rare failure mode.

 

[Cyclomania]

When you say stopped all of a sudden, under what conditions? Riding normal speed on flat ground, riding fast, climbing a hill, etc.? My guess is the BMS tripped and isn’t resetting, possibly due to some weak cell groups, and the 40v measurement is some residual charge from the caps or something, but hearing more about the symptoms may shed more light.
What is your normal charging routine (charge when empty, charge at 20%, etc.)?

It was a normally steep hill. So it was not very steep and I have gone up there many times before. But it had some steepness. Maybe like a 100 meters and an angle of 25%. I think(?) the battery was charged up to about 80-90% or so before it happened. But I am not entirely sure if this with the charging happened earlier so I am not entirely sure if it was charged up since the charger shows green now when charging the battery.

Anyway, it happened close to the top of that hill. The speed might have been like 28km/h or so.
I usually charge it after it has dropped down to about 20-30% since that it where it usually ends up when I have gone to work in the morning, then to training and then home.

Now, a few days ago I know I let it drop very low and it was fully discharged during biking.
Earlier I have also been better at trying to have a "feel" for when the battery is at 90% and stopped charging it at that point. Lately though I have been sloppy and charged it up to a 100% every time I charge it.

Should I open the battery and check the BMS? Or can I still do something else to solve the problem without screwing it open? Where should I attack this problem next? thanks

 

[Cyclomania]

Inspect all the plugs and terminals in your charge and discharge wiring. If one of them got crusty, it will manifest as a large voltage drop that gets worse as more load is applied.

To do this I need to open it right? See if any cables there have gone bad/weak?

If the BMS is the problem as you and E-HP say might be a possible problem, how could I fix this? It the wires, plugs or terminals are not the problem.

Open the battery, change the BMS?

 

[E-HP]

To do this I need to open it right? See if any cables there have gone bad/weak?

If the BMS is the problem as you and E-HP say might be a possible problem, how could I fix this? It the wires, plugs or terminals are not the problem.

Open the battery, change the BMS?

No, I didn’t indicate the the BMS is the problem, I said that the BNS may have tripped due to a problem with the battery, so thee BMS is doing what it’s supposed to do.
Can you post pics of the battery and any labels or printing it may have on it?

 

[Cyclomania]

No, I didn’t indicate the the BMS is the problem, I said that the BNS may have tripped due to a problem with the battery, so thee BMS is doing what it’s supposed to do.
Can you post pics of the battery and any labels or printing it may have on it?

I can't really find any particular specs on it. Only text still left is the one in the picture below that says Shanshan tech(first image).

Has been working fine for about 2 years.

 

[E-HP]

“But today the bike just stopped all of a sudden. And the battery was showing like 5 max 10% charge. I had to walk it home from there.“

Is this based on the display.

 

[electric_nz]

It might be one cell has gone bad, and the BMS is shutting down to protect the rest of the battery. If so the battery won’t work again unless it is replaced. If they are brand name cells (Samsung etc) it’s worth paying for someone to fix, if they are no-name cells then it’s new battery time.

It’s also possible that one cell group has got badly out of balance and needs individually charged.

Either way find someone who can take apart and examine it for you.

 

[eMark]

The charger is showing the green light, for fully charged battery. I have no idea why. Because when I test it with a multimeter it is charged only up to about 40 volts right now. And this is a 48-volt battery.

Being 13s (48v) then 40 volts would be 3.07v for each parallel group. 40v would be considered your LVC ...
54.6v minus 40V = 14.6v
14.6v / 10 = 1.46v ... then 10% of remaining useable voltage (not capacity) would be 41.46v ... 90%of useable voltage would be 53.14v.

Also, when having the charger connected to a wall and the battery connected to the bike, the bike will start. Because it seems the charger can then run current into the bike via the wall.

With you often pulling optimum amps (climbing hills) one of the weaker solder connections finally melted (disconnected) not allowing the BMS to charge ... OR ... damage to at least one of the parallel groups and/or the BMS.

Maybe I rode the battery too close to being completely emptied one day or something?

When you say "emptied" do you mean LVC at 40V (e.g. 0% useable voltage) or even lower than 40V? If possible set LVC of your 13s 48v battery no lower than 41.46 volts.

Anyoe has an idea?

Like others have suggested i'd partially disassemble battery enuf to take voltage readings of each of the 13 parallel groups. See if at least one or more have voltage readings lower than 3.00 volts while other parallel groups voltage readings above 3.07v (13s average
voltage = 40v). Even with bounce back voltage there still should be a significant voltage variance between any weak/bad parallel groups and the remaining useable parallel groups. Check to see if one of the BMS sensing wires is no longer connected.

BEFORE you replace the BMS you first need to check the current resting voltage of all 13 parallel groups.

 

[Cyclomania]

“But today the bike just stopped all of a sudden. And the battery was showing like 5 max 10% charge. I had to walk it home from there.“

Is this based on the display.

This is based on one part the button you can see in the first image. This one usually shows several green spots when fully charged and you press it in for a little bit. Now it shows only one red spot when pressed.

Also, I checked the battery with a multimeter when I got home. It shows around 40 volts. And fully charged(this is a 48 volt battery) I guess it shows around 54 volts or something like that.

Now, the strange part is when current runs through it and it is connected to the charger, in the wall, you can see all the green spots again and it shows 50volts with a multimeter.

So I guess the battery do not "contain" or receive the current that is coming from the charger. But at the same time it seems the cables are not interrupted(?) since when connected to the wall it shows current flowing through the system. And I could even start the bike when the charger was connected to the battery via the wall.

 

[Cyclomania]

Being 13s (48v) then 40 volts would be 3.07v for each parallel group. 40v would be considered your LVC ...
54.6v minus 40V = 14.6v
14.6v / 10 = 1.46v ... then 10% of remaining useable voltage (not capacity) would be 41.46v ... 90%of useable voltage would be 53.14v.

With you often pulling optimum amps (climbing hills) one of the weaker solder connections finally melted (disconnected) not allowing the BMS to charge ... OR ... damage to at least one of the parallel groups and/or the BMS.

When you say "emptied" do you mean LVC at 40V (e.g. 0% useable voltage) or even lower than 40V? If possible set LVC of your 13s 48v battery no lower than 41.46 volts.

Like others have suggested i'd partially disassemble battery enuf to take voltage readings of each of the 13 parallel groups. See if at least one or more have voltage readings lower than 3.00 volts while other parallel groups voltage readings above 3.07v (13s average
voltage = 40v). Even with bounce back voltage there still should be a significant voltage variance between any weak/bad parallel groups and the remaining useable parallel groups. Check to see if one of the BMS sensing wires is no longer connected.

BEFORE you replace the BMS you first need to check the current resting voltage of all 13 parallel groups.

Just open the battery and measure the groups as they are now? See if any cell or cell group looks strange/different?

 

[Cyclomania]

Just open the battery and measure the groups as they are now? See if any cell or cell group looks strange/different?

What tools will I need to check these groups and the bms? (just so I know I have them)

You guys mean open the battery, remove the cover and then measure the individual cells correct? (multimeter?)

Is this risky business? I should have protective glasses?

 

[Cyclomania]

BEFORE you replace the BMS you first need to check the current resting voltage of all 13 parallel groups.

I remember how to check individual cells. How do I check the groups again? Mulitimeter as well right? Check from bottom and top side right? On that whole cell group?

Is this partial dissasemble possible, while not taking of the silicone and adhesives, that makes the cells stick to the cover?? Would be enough to just open the lower battery cover to measure this? Or do I need to take out the whole 13s so it does not stick to the cover at all anymore? To be able to correctly measure this I mean.

thanks

 

[Cyclomania]

I guess the radio silence is because this stuff can be dangerous. But I am in Europe so I would not be able to sue anyone anyway if I did something wrong.

You can give me all the tips on battery builds that you can think of

 

[E-HP]

This is based on one part the button you can see in the first image. This one usually shows several green spots when fully charged and you press it in for a little bit. Now it shows only one red spot when pressed.

interesting. Do you have a pic? It would require 20 LEDs to determine there’s 5% left and 10 LEDs for 10%. I’ve never seen anything like that on a battery or display. I’ve always thought those LEDs were junk, but with that granularity, I may need to reconsider.

 

[Cyclomania]

interesting. Do you have a pic? It would require 20 LEDs to determine there’s 5% left and 10 LEDs for 10%. I’ve never seen anything like that on a battery or display. I’ve always thought those LEDs were junk, but with that granularity, I may need to reconsider.

Not totally sure if it is exactly ten percent. Is around 40-41 volts measured with multimeter. It was hard to take a picture on the little red lamp. But anyway in this picture only a red dot appears to the outer right when you press the button.

I have since I started this thread bought another used battery that had the same bracket mount. Because this battery was a pain. But I still want to fix it now when I have the time.

Only thing I don't exactly understand what you guys mean for me to do. Should I open it and then see if any solders have gotten loose? Measure cellgroups? How do I measure cell-groups? Is that just like measuring a single cell with a multimeter? I do it the same way with plus and minus?

If anything is broken, what do I do from there?

 

[E-HP]

I guess the radio silence is because this stuff can be dangerous. But I am in Europe so I would not be able to sue anyone anyway if I did something wrong.

Not totally sure if it is exactly ten percent. Is around 40-41 volts measured with multimeter. It was hard to take a picture on the little red lamp. But anyway in this picture only a red dot appears to the outer right when you press the button.

Impressive. Yup, batteries can be dangerous. I guess for me, anyone that can determine the state of charge, to that level of accuracy from the status of 4 or 5 dots has abilities far beyond any help I could offer, but there’s lots of other info on the forum and YouTube on battery testing.

I’m glad your main problem is solved and the bike is up and running!!

 

[Cyclomania]

Impressive. Yup, batteries can be dangerous. I guess for me, anyone that can determine the state of charge, to that level of accuracy from the status of 4 or 5 dots has abilities far beyond any help I could offer, but there’s lots of other info on the forum and YouTube on battery testing.

I’m glad your main problem is solved and the bike is up and running!!

I have solved nothing. I did not mean to be smug or anything Nothing is working man I posted because I am asking the guys who knows this stuff. I just want to know what I should do next. I have opened a few batteries but not sure what to look for this time.

 

[E-HP]

As far as radio silence, speaking for myself, batteries are too dangerous, so if I don’t feel confident about the details provided or something doesn’t sound right, I shy away.
That said, here’s a YouTube video I found, searching on checking cell group voltages for an ebike battery.

Be careful.

 

[calab]

Take battery down to lvc and measure the voltage and check the V-delta, right after it reaches lvc.

 

[Dui ni shuo de dui]

I guess the radio silence is because this stuff can be dangerous. But I am in Europe so I would not be able to sue anyone anyway if I did something wrong.

I'm in China so I can't be sued, lol.

Your battery is composed of several cells put in parallel groups and then these groups are put in series with each other. Given the description of the issue, my guess would be that a least one of your cells group died, either because the individual cells that composes it died, or because they got disconnected somehow.

First thing: do not ever charge this battery until you fixed the issue. Seriously. There's a high risk of it catching fire if you do so for too long. Normally your BMS should prevent individual cell overcharge, but you can't blindly rely on it.

First, I suggest you to binge watch as many battery build tutorials as you can on youtube, in order to have a better understanding on how this whole thing works as well as the possible risks, necessary tools, PPE, stuff to do and not to do, etc.
Once you feel confident enough, you can start tearing up the battery.
Measure the voltage of each cell group using a multimeter. Then find the one that doesn't seem to match the others.
Then see if it's technically possible for you to replace this group of cells given your tools and your knowledge.

To be honest it's not as difficult as it might sound, but it is very intimidating.
Also, there's a good chance that replacing just a few cells will only be a short term solution until another group of cells bite the dust, because it's likely that the other cells are gonna die soon.
Take is as a fun project to gain experience with an otherwise dead battery, if you manage to make it work it'll be a cool bonus. If you don't then you'd have still learned a few new skills