Problems with renogy 170ah batteries

[meerkatmag]

Hi, new to this forum but have built a number of solar systems for motorhomes over the years.

I installed 2 x renogy 170ah lifepo4 batteries in my van 18months ago, parallel 12v setup.

They are acting very strange and I wonder if anyone has any idea how to fix them. I've asked renogy for warranty replacement but they are being difficult about it, so not sure it will happen.

Basically, individually the batteries charge up to a certain point, then the battery cuts charging and won't let it get any further. When turning off charger the battery is at about 12.9v. If I apply a load to the battery after a short while it jumps up to 13.3v approx. Both batteries about the same.

It sounds like a cell imbalance with some kind of protection kicking in? I have tried loads of different voltage/current charging runs and so far can't get it to improve. If I run them right down they only last for about 80ah before the voltage is down around 12.5v so I don't think the full capacity is available.

Any ideas what's going on? Or what I can try to get them working?

 

[sunshine_eggo]

The behavior you're seeing is fairly common for batteries to display a lower voltage following over-voltage protection and then showing the correct voltage when a load is applied.

LiTime and a couple other brands have shown the same behavior.

Your batteries are imbalanced. One needs to charge regularly to the balancing level (full charge) to ensure balance is maintained. Manufacturers have different recommendations, but most indicate AT LEAST two hours per month. If your van sits regularly, that would explain it.

A common technique is to hold to 13.8V and/or cycle them to encourage balancing.

It may be worthwhile to break the bank down and test individually.

 

[mikefitz]

sounds like a cell imbalance with some kind of protection kicking in?

Sorry about the similar response, I type slow.

Yes that's what is happening, the BMS shutsdown the charge path, as a result there is a volt drop across the BMS. Applying a load causes BMS recovery.
If you have had this condition for 10s of months its possible the cell inbalance has become worse.
Whet charge profile have you been Using?
Use a charge voltage of 13.8 volts with a long absorbtion period, Renogy have sugested this.
Since you have some method of measuring Ah, estimate how much power you are able to put into the batteries.
A reduction from 340Ah to 80Ah seems unlikely.
13.3 volts could be 70% or over. A small error in measuring voltage leads to a big difference is SOC, 3.35 per cell, 13.4 volts is 97% SOC , 3.25 per cell, 13.3 volts is 70% SOC .
If you have assess to a mains, AC charger, or power supply that you can set to 13.8 volts, subjecting the batteries to this voltage for a few days should cause the balance circuits to have an effect and bring the cells into better balance.

A low cost power meter could be useful in estimating battery capacity,

https://www.amazon.co.uk/MICTUNING-Display-Battery-Monitor-Voltmeter/dp/B07W7XXKVF/ref=sr_1_97?crid=3CCKNKYBIEYV4&keywords=12v%2Bbattery%2Bcapacity%2Bmeter&qid=1702243749&sprefix=12v%2Bbattery%2Bcapacity%2Bmeter%2Caps%2C211&sr=8-97&th=1

Mike

 

[meerkatmag]

Hi, Thanks for the detailed reply I really appreciate it. Its good to know that this behavior is normal when you overcharge protection kicks in. At least its not something worse broken.

Currently the batteries are separate from each other and I'm trying to charge them individually. The 80ah draw test is for a single battery.

Re charging i am using a mains charger, a victron smart charge. if I set the absorption voltage to 13.59 it will get to this voltage and stay there. If I set absorption voltage to 13.6v or above it triggers the overprotection and the battery never gets above 12.9v when disconnected from the charger.

So I can't set it to 13.8 as it will just get to 13.6v and then the battery will cut charge.

I would love to open the case and individually charge the cells but that would void my warranty so for now I'm still hoping they will help.

Is there any point in letting the charger sit at 13.59v on absorption and leave it hoping the bms will self balance?

 

[sunshine_eggo]

Is there any point in letting the charger sit at 13.59v on absorption and leave it hoping the bms will self balance?

Potentially. when at 13.59, does is still flow current or does it slowly taper to 0A.

If it's flowing current, it's still charging, and it's worthwhile.

Effectiveness depends on the BMS. Some BMS only balance during charge and some balance any time cells are > 3.40V and greater than some voltage difference, e.g., if cells are more than 20mV apart.

Hold for 24 hours at 13.59V. Discharge lightly then see if you can increase the absorption voltage a little. If it shows some improvement, then it's balancing by being held at a voltage.

Can you confirm if the batteries spent a lot of time sitting?

 

[Yzman321]

I had four Renogy 170ah batteries in parallel in my camper, I noticed my inverter shut down prematurely on a trip during a deep discharge, and my shunt stated I discharged 240ah out of the 680ah total, or only 35% capacity.

The batteries displayed all the characteristics of imbalanced cells and BMS protection.

I run 12, 24 & 48 volt systems, so I ripped into the cases to see what was what with the cells and found something interesting (I always had a desire to change the BMS on these to get a higher voltage, due to 12v limitations of the BMS). All four batteries had the same issue where cell 1,2,3 is within 0.05-0.1 volts and the fourth cell was always the highest of the group, the highest I seen was 1.35 volts in difference! I believe its a common BMS issue as all four batteries had the exact same issue of significance higher voltage on the 4th cell. The 1.351v delta was 2.449 & 3.800 volts! Much higher than the 3.65v ceiling and 2.449 is at the 2.5v bottom.

Now I have the four batteries in series using a JK 150-amp 20 cell BMS with 1 amp active balancing current. The batteries took 40-50 days to active balance, however now I have 168ah @ 51.2v. If were to do it again I would get the 2-amp active balancing version.

I recommend anyone of know how to do this or change the BMS’s individually. I went with one BMS and put all 16 cells in series. Very easy to do! Hardest thing would be opening the cases as their double lipped and full of glue, the case shatters easily and plastic case shards can fly very fast, best to put on eye protection.

The battery’s main negative is 4 (10 awg If I can remember correctly) wires into the BMS via ring terminals and 4 wires from the BMS to the main negative terminal. I placed a bolt and nut into the ring terminals connecting them & bypassing the original BMS completely, the negative is now long enough to make it the second battery positive for series connection.

The original cell sense wires are long enough to cut and join using a WAGO or similar joiner to connect to the new BMS sense wire. Cut each wire one by one to avoid shorting between cells.

 

[meerkatmag]

Potentially. when at 13.59, does is still flow current or does it slowly taper to 0A.

If it's flowing current, it's still charging, and it's worthwhile.

Effectiveness depends on the BMS. Some BMS only balance during charge and some balance any time cells are > 3.40V and greater than some voltage difference, e.g., if cells are more than 20mV apart.

Hold for 24 hours at 13.59V. Discharge lightly then see if you can increase the absorption voltage a little. If it shows some improvement, then it's balancing by being held at a voltage.

Can you confirm if the batteries spent a lot of time sitting?

Its not flowing any current at 13.59v, it gently drops to zero and stays there.

The batteries haven't really spent that much time sitting. We use the van a lot. I think the batteries were imbalanced from new to be honest, I just didn't know what was wrong. The solar would try to charge them to full but they would cut charge and this would make the system voltage spike to 17v momentarily and my inverter would shut off. This would happen once every minute or so. I didn't know what the issue was and I just turned the charge off when this happened. First time I saw this saw was summer 2022 a few months after I purchased them.

 

[meerkatmag]

I had four Renogy 170ah batteries in parallel in my camper, I noticed my inverter shut down prematurely on a trip during a deep discharge, and my shunt stated I discharged 240ah out of the 680ah total, or only 35% capacity.

The batteries displayed all the characteristics of imbalanced cells and BMS protection.

I run 12, 24 & 48 volt systems, so I ripped into the cases to see what was what with the cells and found something interesting (I always had a desire to change the BMS on these to get a higher voltage, due to 12v limitations of the BMS). All four batteries had the same issue where cell 1,2,3 is within 0.05-0.1 volts and the fourth cell was always the highest of the group, the highest I seen was 1.35 volts in difference! I believe its a common BMS issue as all four batteries had the exact same issue of significance higher voltage on the 4th cell. The 1.351v delta was 2.449 & 3.800 volts! Much higher than the 3.65v ceiling and 2.449 is at the 2.5v bottom.

Now I have the four batteries in series using a JK 150-amp 20 cell BMS with 1 amp active balancing current. The batteries took 40-50 days to active balance, however now I have 168ah @ 51.2v. If were to do it again I would get the 2-amp active balancing version.

I recommend anyone of know how to do this or change the BMS’s individually. I went with one BMS and put all 16 cells in series. Very easy to do! Hardest thing would be opening the cases as their double lipped and full of glue, the case shatters easily and plastic case shards can fly very fast, best to put on eye protection.

The battery’s main negative is 4 (10 awg If I can remember correctly) wires into the BMS via ring terminals and 4 wires from the BMS to the main negative terminal. I placed a bolt and nut into the ring terminals connecting them & bypassing the original BMS completely, the negative is now long enough to make it the second battery positive for series connection.

The original cell sense wires are long enough to cut and join using a WAGO or similar joiner to connect to the new BMS sense wire. Cut each wire one by one to avoid shorting between cells.

This sounds exactly like my issues, the bms in these batteries must be junk. I'll see what renogy come up with, they keep asking me to wait while the technicians think about it. Been waiting a few weeks now.

But when that's all over I will try opening it up. I'm thinking of adding a balancer and leaving the original bms in place as it looks simpler to wire up.

Does the renogy bms balance without charging do you know?

 

[sunshine_eggo]

Its not flowing any current at 13.59v, it gently drops to zero and stays there.

The batteries haven't really spent that much time sitting. We use the van a lot. I think the batteries were imbalanced from new to be honest, I just didn't know what was wrong. The solar would try to charge them to full but they would cut charge and this would make the system voltage spike to 17v momentarily and my inverter would shut off. This would happen once every minute or so. I didn't know what the issue was and I just turned the charge off when this happened. First time I saw this saw was summer 2022 a few months after I purchased them.

Yeah. Voltage spikes are typical when BMS engages protection.

Sounds like they've been imbalanced for a long time.

Still worth trying:

Hold for 24 hours at 13.59V. Discharge lightly then see if you can increase the absorption voltage a little. If it shows some improvement, then it's balancing by being held at a voltage.

 

[JamesRich]

Sounds like another reason to stop buying renogy crap!

 

[meerkatmag]

Sounds like another reason to stop buying renogy crap!

I do regret not waiting for the core batteries, they seem to have a better BMS. I'm a bit annoyed they are dragging their feet in regards to the warranty. They won't let me return it for them to balance, they said I'm not allowed to ship a battery in case it is damaged. But then they don't seem keen to replace them either. Currently I can't really use them so I think that's not right considering I spent £1200 approx on these only 18months ago.

I wonder if the issue is I'm always charging too quickly, YZMan says it took 40+ days to balance, the charging cycle is always pretty quick as I have a 30amp mains charger or 450w solar so perhaps the BMS never has enough time to balance? Really it should have active balancing that happens without charging.

 

[Yzman321]

This sounds exactly like my issues, the bms in these batteries must be junk. I'll see what renogy come up with, they keep asking me to wait while the technicians think about it. Been waiting a few weeks now.

But when that's all over I will try opening it up. I'm thinking of adding a balancer and leaving the original bms in place as it looks simpler to wire up.

Does the renogy bms balance without charging do you know?

To be honest I didn't try to work with the orginal BMS using constant voltage methods. I found it very strange it would have 3 cells completly discharged at 2.5v and the 4th cell overvoltage at 3.8? How would soemthing like that occur by having the pack sit for a period of time like I did, the BMS had to be transferring current while idle.

If you do open the pack, see if your 4th cell was the highest voltage of the 4 cells.

I always searched for internal photos of this battery, or a tear down however never have, so I hope this helps others and adds solutions of what you can do to reuse the good cells. Only thing to note is picture 1 is modified by myself to remove the inline BMS.

 

[sunshine_eggo]

To be honest I didn't try to work with the orginal BMS using constant voltage methods. I found it very strange it would have 3 cells completly discharged at 2.5v and the 4th cell overvoltage at 3.8? How would soemthing like that occur by having the pack sit for a period of time like I did, the BMS had to be transferring current while idle.

For the singular reason that cells go out of balance to begin with:

Different self-discharge rates.

Leave cells sitting unused. They slowly lose charge. They all do so at different rates. Well-matched cells have nearly identical self-discharge rates. Poorly matched cells can lose a top balance in 1-2 weeks. Well-matched cells can retain a top balance for a month or two. MOST will lose a top balance after that. I have four Navitas 3C 25Ah cells that are absurdly well matched. I've let them sit for 6+ months, and they were still within 0.05V when I charged to 14.4V.

The length of time between final assembly and delivery to the customer (typically measured in months) + the requirement to ship LFP at < 30% SoC pretty much guarantees that cheap packaged 12V of any brand will arrive imbalanced.

 

[Yzman321]

For the singular reason that cells go out of balance to begin with:

Different self-discharge rates.

Leave cells sitting unused. They slowly lose charge. They all do so at different rates. Well-matched cells have nearly identical self-discharge rates. Poorly matched cells can lose a top balance in 1-2 weeks. Well-matched cells can retain a top balance for a month or two. MOST will lose a top balance after that. I have four Navitas 3C 25Ah cells that are absurdly well matched. I've let them sit for 6+ months, and they were still within 0.05V when I charged to 14.4V.

The length of time between final assembly and delivery to the customer (typically measured in months) + the requirement to ship LFP at < 30% SoC pretty much guarantees that cheap packaged 12V of any brand will arrive imbalanced.

Have you ever seen a pack do this? This was the worst of the four 170ah Renogy batteries I had. I was able to use the pack in the past without issues, the battery sat for a few months and than it locked all charge and discharge fuctions due to the exterme low and high values.

I am unable to understand how it drifted into 3 cells empty and 1 cell overcharged? Thats why I think the BMS did it somehow, knowing the pack was usable in the past.

Cell 1 2.453 (Cell 09 on JK BMS)
Cell 2 2.495 (Cell 10 on JK BMS)
Cell 3 2.449 (Cell 11 on JK BMS)
Cell 4 3.800 (Cell 12 on JK BMS)

I also confirmed correct voltages on a seperate multimeter, weird right?

 

[Wjm1964]

Renogy seem to have terrible battery management systems and some only allow parallel connection. This guy capacity tested at 0.2C two brand new Renogy Pro batteries with BT and heating and one gave 118Ah (from a 105Ah cell) and i think the other was 108Ah. Bottom line was they both went into shutdown and wouldn't re-charge. The BMS let one cell hit 0.4v and seems pre-set to kill at 10V but with unequal cell discharge rates.

I nearly bought one, glad i didn't.

 

[Tomthumb62]

I had four Renogy 170ah batteries in parallel in my camper, I noticed my inverter shut down prematurely on a trip during a deep discharge, and my shunt stated I discharged 240ah out of the 680ah total, or only 35% capacity.

The batteries displayed all the characteristics of imbalanced cells and BMS protection.

I run 12, 24 & 48 volt systems, so I ripped into the cases to see what was what with the cells and found something interesting (I always had a desire to change the BMS on these to get a higher voltage, due to 12v limitations of the BMS). All four batteries had the same issue where cell 1,2,3 is within 0.05-0.1 volts and the fourth cell was always the highest of the group, the highest I seen was 1.35 volts in difference! I believe its a common BMS issue as all four batteries had the exact same issue of significance higher voltage on the 4th cell. The 1.351v delta was 2.449 & 3.800 volts! Much higher than the 3.65v ceiling and 2.449 is at the 2.5v bottom.

Now I have the four batteries in series using a JK 150-amp 20 cell BMS with 1 amp active balancing current. The batteries took 40-50 days to active balance, however now I have 168ah @ 51.2v. If were to do it again I would get the 2-amp active balancing version.

I recommend anyone of know how to do this or change the BMS’s individually. I went with one BMS and put all 16 cells in series. Very easy to do! Hardest thing would be opening the cases as their double lipped and full of glue, the case shatters easily and plastic case shards can fly very fast, best to put on eye protection.

The battery’s main negative is 4 (10 awg If I can remember correctly) wires into the BMS via ring terminals and 4 wires from the BMS to the main negative terminal. I placed a bolt and nut into the ring terminals connecting them & bypassing the original BMS completely, the negative is now long enough to make it the second battery positive for series connection.

The original cell sense wires are long enough to cut and join using a WAGO or similar joiner to connect to the new BMS sense wire. Cut each wire one by one to avoid shorting between cells.

Wow, thank you. There have been many threads over the last 3-4 years of issues with Renogy lifepo4 batteries. Sometimes it was just a mystery and occasionally after much hullabaloo, Renogy would replace them. And I imagine the replacements had the exact same problem!!

Thank you for taking the time to tear four of these Renogy batteries down and find a common theme. I’ve always had a gut feeling that there was something inherently wrong with the BMS design in these batteries but now you’ve confirmed it.

Would be interesting if someone like Will would do something similar and video the results for the world to see. But thanks for posting what you discovered here.

 

[Yzman321]

Wow, thank you. There have been many threads over the last 3-4 years of issues with Renogy lifepo4 batteries. Sometimes it was just a mystery and occasionally after much hullabaloo, Renogy would replace them. And I imagine the replacements had the exact same problem!!

Thank you for taking the time to tear four of these Renogy batteries down and find a common theme. I’ve always had a gut feeling that there was something inherently wrong with the BMS design in these batteries but now you’ve confirmed it.

Would be interesting if someone like Will would do something similar and video the results for the world to see. But thanks for posting what you discovered here.

Thank you for the acknowledgement!

I myself searched this forum, and other sites like YouTube to find an answer. I am hopeful that everyone who is invested or interested in these batteries see my findings. I believe many of these 170ah batteries have the same issue and could be discarded as defective or "worn out" however the cells are perfectly fine with much use left.

I have two newer Renogy 200ah Bluetooth versions, although I can now see the cell voltages, top balancing is still an issue on both. The Bluetooth app will display one decimal point, one cell will hit 3.6 and the rest 3.3 with the BMS cutting off charging. I never did a capacity test on these however I should soon.

 

[Tomthumb62]

I have two newer Renogy 200ah Bluetooth versions, although I can now see the cell voltages, top balancing is still an issue on both. The Bluetooth app will display one decimal point,

WTF? How is only one decimal point all that useful? I don't know of any other BMS out there that reports cell voltages to only decimal point. Maybe there are some cheapo $10 BMS from aliexpress that do it, but nothing reputable. Renogy's tarred named is only getting worse...too bad, because they were decent once or so I've been told.

 

[740GLE]

It’s probably the software not the hardware that limits to 1 decimal place.

 

[sunshine_eggo]

Have you ever seen a pack do this? This was the worst of the four 170ah Renogy batteries I had. I was able to use the pack in the past without issues, the battery sat for a few months and than it locked all charge and discharge fuctions due to the exterme low and high values.

I am unable to understand how it drifted into 3 cells empty and 1 cell overcharged? Thats why I think the BMS did it somehow, knowing the pack was usable in the past.

Cell 1 2.453 (Cell 09 on JK BMS)
Cell 2 2.495 (Cell 10 on JK BMS)
Cell 3 2.449 (Cell 11 on JK BMS)
Cell 4 3.800 (Cell 12 on JK BMS)

Your example is an extreme, and I expect it is either defective, or it completely escaped any quality control measures where a battery was built with nearly empty and nearly full cells.