Question about a discharged LFP battery.

[100degrees]

Hi all,

I'm building out a backup system to run my medical devices and pond fish pump the one day a year the power cuts off. I'm on grid and have no solar.

I bought 24 LFP batteries. Almost all of them arrived charged to 3.0V. One was at 2.3V. Which is below the normal discharge limit on LFP batteries that I see in a lot of spec sheets. Contacted the seller, they asked me to charge the battery to 3V and see if it held, which it has for the last five days. While that's good, I have some concerns about how discharging an LFP that low might impact number of life time cycles. Should I request a replacement or is this likely to be fine or so minimally harmful that I'll have upgraded the battery system before I ever run into problems given my once a year discharge use case?

Thank you for your time.

 

[sunshine_eggo]

Those aren't batteries. They are cells.

IMHO, you bought from a shady seller. Most reputable vendors ship cells in the 3.25-3.30V range.

My guess is you got bottom-of-the-barrel cells - maybe even used.

 

[100degrees]

Yes, they are cells. My bad.

It's possible. I'm poor so I get what I can afford. As to my question, should I request a replacement on this cell?

Thanks

 

[Rednecktek]

If they charge up and hold the charge, then they're probably fine. Even if you get 99.8Ah out of your 100ah cells, isn't that good enough for the price you paid for them? When you're on a budget getting "close enough" for the savings is just something you have to accept. I bought cheap cells for a couple of my smaller projects knowing that they weren't "EV-Grade-AAA-Super-Perfect-Cells" and they work just fine for my needs. Sure, I'm getting 98.9Ah out of them, but I paid about half what Grade-A cells cost, so good 'nuff for me.

 

[sunshine_eggo]

If they charge up and hold the charge, then they're probably fine. Even if you get 99.8Ah out of your 100ah cells, isn't that good enough for the price you paid for them? When you're on a budget getting "close enough" for the savings is just something you have to accept. I bought cheap cells for a couple of my smaller projects knowing that they weren't "EV-Grade-AAA-Super-Perfect-Cells" and they work just fine for my needs. Sure, I'm getting 98.9Ah out of them, but I paid about half what Grade-A cells cost, so good 'nuff for me.

I'm not talking about this. I bought "EV-Grade-AAA-Super-Perfect-Cells" knowing they were probably not, and I got 95%+ rated capacity from them. Yes. I was happy.

You won't find a single reputable seller shipping cells at 2.3-3.0V. Cells received in that state may very well be used, aren't going to perform, and aren't going to last. They aren't Grade "A" or even "B".

@100degrees

Where did you get these cells?

Size?

Cost?

 

[AshleyL]

Yes, they are cells. My bad.

It's possible. I'm poor so I get what I can afford. As to my question, should I request a replacement on this cell?

Thanks

........It is expensive to be poor, you know........

 

[Rednecktek]

........It is expensive to be poor, you know........

And even with more affordable stuff out there, there's still quite a paywall involved in getting started. Especially when you realize just how energy dense batteries aren't and how much it takes to run loads over time.

 

[100degrees]

If they charge up and hold the charge, then they're probably fine. Even if you get 99.8Ah out of your 100ah cells, isn't that good enough for the price you paid for them? When you're on a budget getting "close enough" for the savings is just something you have to accept. I bought cheap cells for a couple of my smaller projects knowing that they weren't "EV-Grade-AAA-Super-Perfect-Cells" and they work just fine for my needs. Sure, I'm getting 98.9Ah out of them, but I paid about half what Grade-A cells cost, so good 'nuff for me.

I don't fully understand how internal shorting works. Do cells catch fire if they've been over discharged and then put into use or do they simply self-discharge more rapidly? If they're safe the capacity really isn't a problem.

 

[100degrees]

I'm not talking about this. I bought "EV-Grade-AAA-Super-Perfect-Cells" knowing they were probably not, and I got 95%+ rated capacity from them. Yes. I was happy.

You won't find a single reputable seller shipping cells at 2.3-3.0V. Cells received in that state may very well be used, aren't going to perform, and aren't going to last. They aren't Grade "A" or even "B".

@100degrees

Where did you get these cells?

Size?

Cost?

They're these: https://batteryhookup.com/products/...4-prismatic-cells?_pos=1&_sid=ab700c234&_ss=r

 

[100degrees]

........It is expensive to be poor, you know........

I am very aware of this fact. Unfortunately, with my health issues, I have no other choice.

 

[100degrees]

And even with more affordable stuff out there, there's still quite a paywall involved in getting started. Especially when you realize just how energy dense batteries aren't and how much it takes to run loads over time.

Agree. What I usually do is get the minimum that will do what I need with some level of dependability and then learn how to build every part of it from scratch. I don't have money. I do have time.

 

[AshleyL]

I am very aware of this fact. Unfortunately, with my health issues, I have no other choice.

Birds of same feather eh?

Anyway, the only way to find out the current condition for those cells is to do a complete capacity test and measurement of internal resistance at different voltage stages. I doubt you have the necessary tools for it, but at least tell us that you have proper BMS with active balancer built-in?

 

[100degrees]

Birds of same feather eh?

Anyway, the only way to find out the current condition for those cells is to do a complete capacity test and measurement of internal resistance at different voltage stages. I doubt you have the necessary tools for it, but at least tell us that you have proper BMS with active balancer built-in?

I can probably build something to do capacity tests. Unless capacity testing is more complicated than it seems. Maybe something like this: https://www.instructables.com/Li-ion-Capacity-Tester-/ with nichrome wire rather than a ceramic resistor.

My setup is 24 of those LEV60F cells 8S 3P run through a Daly 150A 24V 8S BMS to a Midnite MN3024DIY. I'm still trying to figure out fusing. The charge controller has a built in 150 amp fuse but I'd like to fuse the individual cells and maybe limit maximum output before the Daly to twice my expected draw. This system should only ever see a combined load of about 250 watts other than the inductive surge when the pond pump first starts.

 

[DIYrich]

They're these: https://batteryhookup.com/products/...4-prismatic-cells?_pos=1&_sid=ab700c234&_ss=r

The cells are rated 2.0-3.5v. You received the cell in that range. It should be ok. Do a charge and capacity test. If tests fine, it should be ok.

 

[AshleyL]

I can probably build something to do capacity tests. Unless capacity testing is more complicated than it seems. Maybe something like this: https://www.instructables.com/Li-ion-Capacity-Tester-/ with nichrome wire rather than a ceramic resistor.

My setup is 24 of those LEV60F cells 8S 3P run through a Daly 150A 24V 8S BMS to a Midnite MN3024DIY. I'm still trying to figure out fusing. The charge controller has a built in 150 amp fuse but I'd like to fuse the individual cells and maybe limit maximum output before the Daly to twice my expected draw. This system should only ever see a combined load of about 250 watts other than the inductive surge when the pond pump first starts.

Hmm.....Daly BMS..........I suggest you to buy one active balancer such as NEEY 4A too to keep the cell in balance after full top balancing manually.

 

[upnorthandpersonal]

I've attached the 'datasheet' for these cells to this post. Seems these are rated from 2.0V to 3.5V, so give them a go. I'm not sure what they did with the chemistry in this particular LFP cell, but could be ok. Only way to really find out it with a capacity test.

 

[sunshine_eggo]

These are still LFP cells. When LFP first came out, they operated from 2.0 to 4.2V. They found this was quite detrimental to the cells, and cycle life was dramatically reduced, so the range was limited to 2.5-3.65 sacrificing about 15% capacity for dramatically improved cycle life.

No matter what the datasheet says, don't run them to 2.0. It doesn't make receiving cells at 2.3 or 3.0V okay.

I literally just made a purchase from BH, so I'm not down on them, but that doesn't mean I think the cells are trustworthy. Nor do I think BH does thorough testing. They sample test them and ship them out. I don't think they would knowing send cells out at 2.3V, so I bet they didn't even check the voltage.

EVERYTHING from BH should be tested for capacity, internal resistance and self-discharge.

I have some concerns about how discharging an LFP that low might impact number of life time cycles.

This is completely valid, and only time will tell. These are allegedly new and unused. In my experience with thousands of batteries/cells, outliers are ALWAYS the problems. Out of 24 cells, you received a notable outlier. I would personally insist on a replacement.

 

[100degrees]

The cells are rated 2.0-3.5v. You received the cell in that range. It should be ok. Do a charge and capacity test. If tests fine, it should be ok.

I'll do that once I have a capacity tester. Thanks for sharing your thoughts on this.

 

[100degrees]

Hmm.....Daly BMS..........I suggest you to buy one active balancer such as NEEY 4A too to keep the cell in balance after full top balancing manually.

If you don't mind could you please explain what you mean?

Prior to buying the Daly I watched the video series put together by Off Grid Garage on youtube where, over the course of three videos, he tries to understand how Daly balances. He ultimately concludes that it does so by discharging all but the lowest cell at 30ma until all cells or cell banks are equal. Presumably when the bank is then recharged the cells will be very close to the same level of charge. He then mentions that this is a silly way to do things. While I agree with him, Daly is well documented and what I could get. I also felt that even this inefficient solution to balancing was perfectly adequate for my use case as a once-a-year battery back up. I'll be wasting more power with the MN3024DIY, even in sleep mode, than the balancing process will consume. If I'm missing something please help me out by explaining where I'm going wrong.

 

[100degrees]

I've attached the 'datasheet' for these cells to this post. Seems these are rated from 2.0V to 3.5V, so give them a go. I'm not sure what they did with the chemistry in this particular LFP cell, but could be ok. Only way to really find out it with a capacity test.

Never occurred to me to even look for the datasheet. Thank you very much for finding and posting this.