I have a 6 year old installation in a 4 x 5kW Axpert Inverter setup as attached with 20 x Pylontech US2000 Plus (And some new US2000C Top batteries in Cabinets for failed US2000C Plus Replacements). US2000 Plus Batteries started failing 1 or 2 at a time since 2 years ago with 900-1100 cycles on the batteries. Initially when installed in 2017 Pylontech approved the 53.2v Float/Absorption charge settings for the 10 year warranty and it was submitted to them by installer. 2 Years ago they replaced 2 batteries. The voltages on inverters was then adjusted by installer due to 2 batteries failing to a lower voltage 52.7v Absorption and 52.4v float, according to installer Pylontech's new recommendation is lower voltages to prevent overvoltage which still indicates the batteries are charged 100% full after the settings changed, so voltages seemed fine.  Earlier this year another 2 batteries started to discharge faster than other's and Pylontech did not replace it and attributed it to overcharge voltages. How can 2 batteries in 2 cabinets fail out of 20 (4 x 5 Strings of batteries, 5 batteries per inverter) Insurance declined physical or electrical damage claim and attributed it to wear and tear. Pylontech should cover battery usage (Wear and Tear) for 10 years correct ? If warranty not covering these batteries and insurance not covering it under electrical/surge damage does anyone have a resolution here please ? Last week I noticed another battery discharging faster than other's and since Pylontech is not replacing I opened it to check if swollen. It was swollen as attached as the previous ones which they did not replace so I did not care I if voided the warranty by opening it. Today another US2000 Plus started discharging faster than other's. Some sample monitoring screenshots attached. The 10V Battery on the left side of image attached was swollen, on other 2 batteries the 30V right side was swollen. Totally random and different inverters on these batteries. All battery cycles since installed 6 years ago are less than 1200 Cycles. Since day 1 battery monitoring was done (1st ICC then then swopped to Solar Assistant), battery voltages never exceed 53.2v and the past year never exceeded 52.7v after lower voltages set on inverters. Cut-off voltage done before reaching minimum voltages around 20% battery remaining on cut-off but low voltage according to Pylontech warranty replacement was not the problem, overvoltage was. Battery temps as per 3 months graphs indicates battery temps are within suitable temp ranges. I can only monitor 8 batteries at a time due to US2000 Plus limitations but I swop the monitoring console cable to a different set of batteries every 3 or 4 months to check if batteries still good. So 6 Batteries failed out of 20 and Pylontech attributes this to overvoltage and only 2 replaced. 1 I opened so voided warranty and the one I checked today not opened yet. Any ideas since I will rather not recommend Pylontech for honoring their 10 years warranty at this stage. I also queried them dates of which overvoltages occured but they just ignored me.

40 minutes ago, JT1 said:

I have a 6 year old installation in a 4 x 5kW Axpert Inverter setup as attached with 20 x Pylontech US2000 Plus (And some new US2000C Top batteries in Cabinets for failed US2000C Plus Replacements). US2000 Plus Batteries started failing 1 or 2 at a time since 2 years ago with 900-1100 cycles on the batteries. Initially when installed in 2017 Pylontech approved the 53.2v Float/Absorption charge settings for the 10 year warranty and it was submitted to them by installer. 2 Years ago they replaced 2 batteries. The voltages on inverters was then adjusted by installer due to 2 batteries failing to a lower voltage 52.7v Absorption and 52.4v float, according to installer Pylontech's new recommendation is lower voltages to prevent overvoltage which still indicates the batteries are charged 100% full after the settings changed, so voltages seemed fine.  Earlier this year another 2 batteries started to discharge faster than other's and Pylontech did not replace it and attributed it to overcharge voltages. How can 2 batteries in 2 cabinets fail out of 20 (4 x 5 Strings of batteries, 5 batteries per inverter) Insurance declined physical or electrical damage claim and attributed it to wear and tear. Pylontech should cover battery usage (Wear and Tear) for 10 years correct ? If warranty not covering these batteries and insurance not covering it under electrical/surge damage does anyone have a resolution here please ? Last week I noticed another battery discharging faster than other's and since Pylontech is not replacing I opened it to check if swollen. It was swollen as attached as the previous ones which they did not replace so I did not care I if voided the warranty by opening it. Today another US2000 Plus started discharging faster than other's. Some sample monitoring screenshots attached. The 10V Battery on the left side of image attached was swollen, on other 2 batteries the 30V right side was swollen. Totally random and different inverters on these batteries. All battery cycles since installed 6 years ago are less than 1200 Cycles. Since day 1 battery monitoring was done (1st ICC then then swopped to Solar Assistant), battery voltages never exceed 53.2v and the past year never exceeded 52.7v after lower voltages set on inverters. Cut-off voltage done before reaching minimum voltages around 20% battery remaining on cut-off but low voltage according to Pylontech warranty replacement was not the problem, overvoltage was. Battery temps as per 3 months graphs indicates battery temps are within suitable temp ranges. I can only monitor 8 batteries at a time due to US2000 Plus limitations but I swop the monitoring console cable to a different set of batteries every 3 or 4 months to check if batteries still good. So 6 Batteries failed out of 20 and Pylontech attributes this to overvoltage and only 2 replaced. 1 I opened so voided warranty and the one I checked today not opened yet. Any ideas since I will rather not recommend Pylontech for honoring their 10 years warranty at this stage. I also queried them dates of which overvoltages occured but they just ignored me.

Well, Pylontech buys these cells from some Chinese manufacturer or two or three. The manufacturer gives a guarantee for the cells, but it is probably just made up, thumb suck. Pylontech then puts a thumb suck guarantee on their batteries, hoping for the best. They also know they cannot put a short guarantee as their batteries won't sell, so they put an inflated 10 year guarantee to compete with other battery manufacturers that thumb suck as well. Now after all this thumb sucking the thumb is no longer in good condition. If things go wrong, which most likely it will, they will just insist that the customer is at fault, stuff like like overvoltage, bad battery temp, overcharging, undercharging, etc, whatever they can thumb suck to get out of a claim.

I'm not sure any other brand would have given you significantly better service. My system is about 5.5 years old now, but the batteries are younger. This is because I originally had a different brand of battery. Let's call them BrandX and say that they were replaced with Freedom Won.

Anyway, round about the 3 year mark the BrandX batteries started showing much quicker drop in SOC under load when there was no PV. OK... so I understand that things decay and don't last forever, and, like most of us, this is my first PV system and I'm still learning what it is to live with this system, and for all I know this is a usual drop in performance after 3 years. 

So I asked BrandX (which gave them a way to pre-empt the shenanigans that followed) and my installer: Is this a usual drop off of performance after 3 years? If I'd been told yes, I'd have filed this away under "lessons learned", and would have adjusted some timer switches to run some loads a bit later in the day when PV is available. 

But nobody would give an answer to that question. Instead BrandX took my batteries away for testing leaving me with no protection (and implying a response of "no" to my question), but I suppose it's fair to let them examine and test if it's a potential warranty claim. They then said that the batteries were absolutely fine, so I asked them to explain the change in performance - which I could show. They then sent technicians out who plugged in some diagnostic software and said I'd been overcharging. I asked them why they'd said the batteries were OK and are now saying that actually they are damaged and have been misused.

No answer.

Then I asked to see the data. There was an overcharge event in the log but 
1) it was in excess of what my inverter can deliver to (or demand from) the batteries
2) it predated my purchase of the batteries

Anyway... we danced a few times around the floor with no definitive answers to any questions. 

I eventually concluded that all this stuff about 10 year warranties is not worth what it's printed on because nobody's been in this game for 10 years anyway. So what does anybody know?

Not much comfort for you there, I'm afraid. I am a bit jealous of your setup because you have multiple small batteries, so if one or two go belly up or have to be taken away then you still have some protection. I currently have one Freedom Won 10/8, and if they want to take that away for testing then I am left with nothing.
 

1 hour ago, JT1 said:

I have a 6 year old installation in a 4 x 5kW Axpert Inverter setup as attached with 20 x Pylontech US2000 Plus (And some new US2000C Top batteries in Cabinets for failed US2000C Plus Replacements).

Just curious - do you have those Axperts running in parallel, with all the 20 Pylontechs in parallel too?

Or is it one Axpert per five Pylontechs, separated into four groups?

Edited November 4, 20241 yr by Youda
spelling

It is 5 x batteries per inverter and 4 inverters in parallel. All have the same kWh of batteries 12kwH per inverter (5 x 2.4kW). I am sure these cells are not that good if it has swollen on each failure even after voltages was dropped a year ago, why are some still failing after 1000-1200 cycles. Inverters never run past 60% (3kW) per inverter, I have added a breaker on DBBoard to ensure inverters utilisation 60-65%% is never exceeded. I think the 3000 cycles is just a thumb suck. So I opened the one discharging faster as well this morning and batteries also swollen, another R 30k down the drain for the 2 batteries since last week.  It seems to happen to random batteries every 8 months now the past 2 years, total of 6 US2000 Plus lost now out of the 20. Replaced with US2000C but I am thinking of just living with the remaining ones until all of them die and then check another brand, but all battery brands probably same. Waste of an investment, ROI is only due in about 4 years since it was a large system to start with due to more than average home power usage, but in a loss with these battery failures.

Edited November 4, 20241 yr by JT1

29 minutes ago, Bobster. said:

I'm not sure any other brand would have given you significantly better service. My system is about 5.5 years old now, but the batteries are younger. This is because I originally had a different brand of battery. Let's call them BrandX and say that they were replaced with Freedom Won.

To be clear: BrandX is not PylonTech.

 

Thanks for the answer. So the inverters are in parallel on the AC side and all the batteries are connected in parallel too, in a common DC BUS?

 

45 minutes ago, JT1 said:

Replaced with US2000C but I am thinking of just living with the remaining ones until all of them die and then check another brand, but all battery brands probably same. Waste of an investment, ROI is only due in about 4 years since it was a large system to start with due to more than average home power usage, but in a loss with these battery failures.

I am using Pylontech too (16 x US3000), since I was looking for a rack form-factor and by the time I bought first one, Pylontech was the only manufacturer with a rack-mount option. As of today there are dozens of rack-mount alternatives to choose from.

So far mine are running okay, but they have just 5 years  and much less than 1000 cycles (can check the exact cycles later).

Anyway, for the future it might be better to choose a manufacturer that is using standard prismatic cells with the screw terminals. Should some of the cells fail, one would be able to buy the replacement anywhere and then just plug it in and rebalance.

(Problem with Pylontech is that they are using 25Ah pouch cells, where US2000 has two connected in parallel, US3000 has three, etc. This design is basically non-repairable and prone to self-destruction in a case that one of these paralleled pouches is weaker than the other. Problem with some other manufacturers is, that even when they are utilizing prismatic cells, their terminals are welded, therefore quite hard to replace.)

 

 

 

Reading carefully, it seems that @JT1's batteries are in 4 separate banks, one for each inverter.

If this is the case it is wrong and may explain some of the issues.  All batteries should be in parallel, feeding all the inverters, normally via a busbar.

As I understand it the Master inverter manages current and voltages for all the inverters, based on SOC/Voltage the batteries it is connected to.  That means that the slave inverters will be controlled based on SOC/Voltage of the bank connected to the master, which is very likely to be different if they are not connected in parallel. 

Axpert inverters are notorious for overshooting charge voltage targets at the best of times - introducing an error of this type will certainly make matters worse.  I am a bit surprised that your Pylons lasted this long

One point: while @Youda is 100% correct saying that these batteries are almost irreparable, it is quite easy (WITH GREAT CAUTION) to swop out the packs of 10 cells (5x2).  So, if you have 3 batteries each with one bad pack you can at least make two good ones from the three.  An added bonus is that your batteries are all the same age.

Edited November 4, 20241 yr by Calvin

@Calvin Thanks for the feedback, but from my knowledge and testing the inverters handle charge rates of batteries (and draining of batteries) on their own even if in parallel and not from SOC on Master. E.g Currently due to 2 Bad batteries out of the 20 installed (4 Inverters x 5 Pack Batteries per Inverter, 2 Inverters only have 4 Batteries due to random 1 failing on random 2 inverters which I removed). The Max grid charge current and Max charge current (Total for PV + Utility) is set individually on each inverter (and does not populate like some other settings to other inverters in parallel). Max charge rate is currently set at 80A since if I remove a battery I do not want each battery to charge more than 20A per battery.

Attached Screenshot shows Battery Pack Voltage for any inverter is within 0.1-0.2 volt from each other (When draining and when charging as attached) and each inverter battery voltage never exceeded the absorption voltages set currently of 52.7v (Float 52.4v). This Absorption still allows 0.5v over charge for max 53.2v if axpert charging rates spiking as some people claim the inverters does, but I have not seen it personally. The Highest Voltage Battery 5Pack per Inverter also drains more power from battery pack to get to equal voltages with other packs as per screenshot and is per inverter based. The same goes when charging, all battery packs per inverter stays within 0.1-0.2v from each other even if 4 batteries per 2 inverters at this stage and 5 batteries in other 2 cabinets for 2 inverters. i.e when battery amount is different the inverters still handle charge voltages each on their own to be same for each inverter. Report for past 3 months attached and a live screenshot.

Victron recommends lower charge voltages compared to Pylontech 53.2v as at https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom which I have set more than a year ago. But still Pylontech/SegenSolar attributes the damage to overvoltage and insurance attributes it to wear and tear (Which Pylontech should cover). I think these batteries are only good up to around 1000-1200 Cycles. During any of the batteries lifetime it has been drained to cut-off voltage less than 10  times I estimate, when we had a few days power outages and then raining the those days and pv panels not charging to float each day it went to cut-off voltage a few times. My DOD is set to 40% and if SOC on 60% I start charge from Solar + Utility Simultaneously via Home Automation (Home Assistant MQTT Rules). Other HA rules also regulates batteries during night or when PV Panels have a low charge rate and never drained more than 60Amps PER 5 Pack.

For info I am also driving an EV as a daily driver and the battery has a 8 years warranty. Will XXX Motor Vehicle company do the same and attribute battery failure to overvoltage (from their own installed chargers) if the battery fails and get's swollen (And it is underneath the car installed...maybe the seat will rise in a year or 2 lol). Just wondering about these thumb suck battery lifespan issues, currently the distances I travel the battery should last between 50 - 60 years before reaching 3000 Cycles. But only time will tell how they will handle a failing battery and hopefully not the same as Pylontech does and not honoring their wear and tear warranty on a battery that has been well looked after.

 

Edited November 5, 20241 yr by JT1

@JT1 Correct me if I am wrong:

All the installation manuals that I have read (both from Voltronics and Pylontech) says that your installation should have had all the batteries connected to all the inverters (and ideally all the batteries to a Pylontech LV hub)

You decided for whatever reason to do it differently.  Now, your batteries are going legs-up and you are complaining.

Perhaps the batteries would have died anyway, but if you do not follow the manufacturer's installation instructions, I do not think that you have a valid complaint.

For what it is worth, I can see the logic in connecting the batteries together as per manufacturer's instructions.

Edited November 5, 20241 yr by Calvin

@Calvin A Certified Installler did the initial installation. I did the monitoring and home automation to take care of batteries minimum 60% SOC and still logged the return of batteries via the installer to Segensolar. I did not decide for whatever reason to do it differently, that was done by installer who communicated with Segensolar who he purchased the batteries from. Pylontech approved the battery warranty on the installation and I can attach the warranty certificates if needed. If installation was an issue why is random batteries failing now reaching ±1000-1200 Cycles. If installation was bad why only 6 out of 20 batteries failed. Other's SOH still above 92% after 6 years in same configuration.

Edited November 5, 20241 yr by JT1

@JT1 

25 minutes ago, JT1 said:

A Certified Installler did the initial installation

Sadly this industry is awash with tales of "certified installers" who are not competent - read this forum for many examples.

 

25 minutes ago, JT1 said:

If installation was an issue why is random batteries failing now reaching ±1000-1200 Cycles. If installation was bad why only 6 out of 20 batteries failed. Other's SOH still above 92% after 6 years in same configuration.

A bad installation does not guarantee instant failure - abused batteries will simply have a shorter lifespan.  Whether abused or not, "identical" batteries will not all fail at the same time.

 

25 minutes ago, JT1 said:

Pylontech approved the battery warranty on the installation and I can attach the warranty certificates if needed.

Irrespective of all the certificates, the fact remains that the installation is wrong.  I would take it up with the installer (assuming he is still in business...), but either way I would get it corrected.

Edited November 5, 20241 yr by Calvin

This is how it should be connected on the BAT side, according to the Axpert Paralleling Guide:

 

But maybe that it IS connected like this in reality, and @JT1 just don't know it, since he was not the one who did all the DC wiring.

Anyway, batteries went belly-up, Pylontech's legendary 10-years warranty proved itself being non-existent => time to rip it off and replace with something better. 😕

 

1 hour ago, Youda said:

But maybe that it IS connected like this in reality, and @JT1 just don't know it, since he was not the one who did all the DC wiring.

Except, if you look at the last picture in his first post, there was a 0.7V difference across the 4 batteries shown with very little current flowing.

Difficult to imagine if they are all connected in parallel.

Edited November 5, 20241 yr by Calvin

1 hour ago, Youda said:

Pylontech's legendary 10-years warranty proved itself being non-existent

Maybe a little harsh: they did replace 2 batteries under warranty, despite them being installed incorrectly.

@Calvin, Remember on first image Pack #1 - #5 is connected to Inverter 1 and Pack 6-10 (of which only 6,7,8 in image due to 8 limit on monitoring) is connected to inverter 2 hence why the 3 batteries are at different charge states as opposed to Pack#5 (pack 1 to 5 is at same voltage levels managed by inverter 1 which is 0.1-0.2v apart on batteries). Monitoring cables are split across cabinets but that does not influence charge rates per inverter and balancing battery voltages per inverter. Charge rates differ from each inverter and it will charge as per set max absorp and max float. I will check to add a bus bar but from stats I see batteries are within 0.1-0.2v from each other per inverter 5 packs. I maintained these batteries well on temps & DOD but seems 1000-1200 Cycles max. Only time will tell Pylontechs quality or if Wiring issue since I have 2 x US3000C on a single Inverter for 2 years now at another property and 2 x US2000b plus for around 3 years at a 3rd location. I do not monitor these batteries daily as with my own home batteries. I will remove the US2000b Plus next week and check max and min cell voltages on full charge on a monitoring system or via BatteryView and drained charge since it was installed on a single inverter since purchased.

Edited November 5, 20241 yr by JT1

You need to download the log files from the batteries with BatteryView- that is the only and definitive way to see if the batteries have suffered over voltage.

15 hours ago, Calvin said:

Axpert inverters are notorious for overshooting charge voltage targets at the best of times - introducing an error of this type will certainly make matters worse.  I am a bit surprised that your Pylons lasted this long

Sadly this is big problem in a lot of systems, as can be seen often in this forum.

Edited November 5, 20241 yr by Tinbum

22 hours ago, JT1 said:

I will check to add a bus bar but from stats I see batteries are within 0.1-0.2v from each other per inverter 5 packs.

@JT1 I am obviously not expressing myself clearly - let me try again:

Of course the batteries in each inverter pack are at approximately the same voltage - they are after all connected in parallel. The busbar I am talking about would be there to connect all the different packs together, so that all the packs are also at the same voltage.  You need one large battery pack for your 4 paralleled inverters, not 4 separate ones at potentially different voltages.

I went through the remaining 18 Batteries. A single US2000B+ out of the 18 has a single faulty cell (Cell 7 in attached overvoltage / 0v every 10 seconds) while all other batteries are fine. This could cause one of the 3 battery packs inside pylontech to get swollen over time. I.e 15 cells per battery * 18 US2000b+ which is 270 total cells on the installation and 1 cell has an issue on a random battery and it is attributed to a faulty installation ? All the log files exported from all US2000b+ overvoltage less than 10 times in 6 years, which can easily occur on any inverter in 6 years. Pylontech market their products for overvoltage protection and it should do the job, so a 3rd battery dead since charging is stuck at 1% charging due to one faulty cell. In total 7 batteries of 20 failed in 6 years. 

I am sure v1.1 Firmware is also a problem and has it's flaws since 6 years later we are on v3.4 (23?? firmware updates released to address issues?, or less perhaps) for US2000b+, but still it was/is not perfect on v1.1 on doing what it is supposed to for the built-in protection. I will contact Pylontech to get all updated since v1.1 was definitely not perfect on overvoltage and other functions described as a sales pitch to buy their batteries.

Edited November 6, 20241 yr by JT1

@Calvin, yes I know battery volts will be same per inverter in parallel but you pointed out the 0.6v difference per inverter battery set hence why I made it clear Pack#5 is on a different inverter as per screenshot. If e.g Inverter 1 batteries are at 100% and [email protected] and inverter 2 batteries is at 95%, Inverter 2 will still charge at it's own rate. I can see 0A going from Inverter 1 to batteries from monitoring logs when it's battery set at 100% since it has reached it's set float volts . But inverter 2,3 or 4 then charges each at different amps depending on their battery set SOC. Each inverter charges at it's own amps (which is ALWAYS different on real-time monitoring per inverter) if batteries not at 100% and I see x Amps going to batteries, but fully charged batteries 0 amps flowing to it. i.e per Inverter batteries does not get overcharged since the inverter will stop for it's set of batteries when reaching float. I cannot see how batteries can be overcharged/overvolted or has been overcharged from any logs or real-time monitoring. Parallel inverters share the load, but also according to battery SOC Levels and power delivered from each inverter when on batteries never the same Watts to ensure batteries drain at the same pace.

Edited November 7, 20241 yr by JT1

Hi all, to add my 2 cents. I have recently had 5 x 2000’s returned to the supplier for evaluation. Installed in 2020 and registered with Pylontech for extended warranty. Two batteries recently started flashing alarm with no charge occurring and I contacted my installer as a result. The 2 batteries in question were horrendously swollen and the other 3 already starting to burst casings. I don’t have any graphs or further information. Only that I had what I believe was a good installer install my system (recommended by Solar Advice) and never played with anything i shouldn’t. I never pushed the batteries all that hard nor had more than a few trips on the inverter. 2 batteries to 1 x 5kw Deye and 4 batteries to another 5kw Deye covering 2 of my 3 phases. 1 battery seems to be ok at present. Patiently waiting for a view from the supplier with a way forward. 

@iMercury Wow those cells are heavy swollen when a case is starting to tear. I have checked the other 2 Pylontech installations I have running from a single inverter and downloaded log files. The US3000C x 2 Batteries installation on single inverter is fine, Cycles 450/459 between the 2 batteries and no errors. The US2000C Single Inverter Installation (EXACT Same inverter as on US3000C Installation) however is one battery attached. I can see it is swollen and logfiles indicate Cell HV, LV, UV and no power overvoltages. I.e Inverters did not overcharge and all PWR Counters on 0. Only 1 of the US2000C in parallel is going belly up. Sad thing about this US2000C it only had 202 Cycles. Pylontech will Replace this. I already had a great installer (well known on the forums) had a look at the logfiles and he also mentioned it is cell issues and not installation or charging/discharging issues. It seems there is definitely a problem on specific batches of US2000?? Cells. The other US2000C below, 191 Cycles is running normally (3 HV Cells Logged at a specific time will not bother me to send in for replacement though)

Swollen US2000C:

Bat OV Times    :    23852
Bat HV Times    :      401
Bat LV Times    :      322
Bat UV Times    :      127
Bat SLP Times   :        0
Pwr OV Times    :        0
Pwr HV Times    :        0
Pwr LV Times    :        0
Pwr UV Times    :        0
Pwr SLP Times   :        0

Good US2000C in Parallel with above battery since day of installation:

Bat OV Times    :        0
Bat HV Times    :        3
Bat LV Times    :        0
Bat UV Times    :        0
Bat SLP Times   :        0
Pwr OV Times    :        0
Pwr HV Times    :        0
Pwr LV Times    :        0
Pwr UV Times    :        0
Pwr SLP Times   :        0

On 2024/11/04 at 9:02 PM, Calvin said:

Axpert inverters are notorious for overshooting charge voltage targets at the best of times - introducing an error of this type will certainly make matters worse.  I am a bit surprised that your Pylons lasted this long

Ah shit, i have an Asxpert Max and i have planned to have 5x US2000 Plus batteries for a first time. Bad choice ? I should migrate to prismatic ?

 

On 2024/11/04 at 11:55 AM, Youda said:

(Problem with Pylontech is that they are using 25Ah pouch cells, where US2000 has two connected in parallel, US3000 has three, etc. This design is basically non-repairable and prone to self-destruction in a case that one of these paralleled pouches is weaker than the other. Problem with some other manufacturers is, that even when they are utilizing prismatic cells, their terminals are welded, therefore quite hard to replace.)

I have also an US2000 Plus with swollen batteries and i am trying to replace the pouch cells with new ones. Not economically viable ? 

 

21 hours ago, fhocorp said:

I have also an US2000 Plus with swollen batteries and i am trying to replace the pouch cells with new ones. Not economically viable ? 

Well, cells themselves are pretty cheap, as one 25Ah LFP pouch cell costs just around 25 USD. Just remember that finding a cell with the same dimensions on the market might be a bit challenging, of course.

But the main problem is that the Pylontech repair will be quite a messy work:

• There are three cell packs in the US2000, each one sealed in plastic.
• Internal wiring of the each cell pack is 5S2P.
• You can't replace just one swollen cell, but at least the two that are connected in parallel.
• Chances are that some other pairs in the pack(s) will be swollen too.
• Chances are that all three cell packs will contain swollen cells.
• You have to carefully cut open everything, diagnose, unsolder/solder, and re-pack the cells tight, in order for them to fit back in.
• Not to mention that you have to precharge all the cells in the battery to the same voltage, as the internal balancer is not powerful enough to solve bigger voltage differences.

IMHO, much easier approach would be to buy US2000 with a dead BMS board and just swap a swollen cell pack for the salvaged one.

 

It's important to keep in mind that the cells are swelling for a reason:

• Overcharge, undercharge, overheat, etc.
• If you do not remove root cause of the failure, there's no point in fixing the batteries as they will get killed again.
• Most of the time it's like this: one or two cells are extremely swollen, while the rest of them is starting to swell too.
• A case of 29 perfect cells sitting in a box with the one that's looking like a balloon is .....unrealistic.

 

Personally, I run a lot of Pylontechs too. Should they start to die, I will go for something with prismatic cells inside, as swapping a prismatic cell with the screw terminals is "a piece of cake" when compared to brain surgery skills needed for the Pylontech.