Is my 12v LiFePO4 Battery dead?

I have a 12v 80AH LiFePO4 battery that has been sitting for 5 months. Yesterday I charged it up and after a few minutes it read full and the resting voltage reads 13.4v.

Today I wanted to test it, so I put a 5A load on the battery expecting it to last 10hrs before I disconnected the load. I went back to the battery after 1 hour and the battery was basically dead. The voltage only read 0.6v.

Then I put the battery back on the charger and after 30min it said fully charged again.

So is this battery pack dead? Is it possible that there is just some problem with the BMS?

I've read that if the battery wasn't charged over the course of a few months that the cells may have become unbalanced and the BMS can't correct it. Does it sound like this could be the case here and if so how do I rebalance the cells?

Sounds like it's imbalanced, the .6V reading was just the BMS turning off the discharge when a cell group reached low voltage.

Charge it, then check the individual cell group voltages, you probably have one that's substantially lower than the rest.

You should be seeing around 14.4V on a full charge (3.6V x 4 cell groups), the fact that it's stopping well before that tells me there's probably at least one cell group that's lower than the rest. The BMS cuts off charging when one of the cell groups reaches full charge, then it tries to drain down that full group to allow charging to continue on the remainder. On an 80Ah pack that could take a very long time, so when the imbalance is severe it's easier to manually bring the low group(s) up with a single cell charger of some sort.

dustNbone said:

The BMS cuts off charging when one of the cell groups reaches full charge, then it tries to drain down that full group to allow charging to continue on the remainder. On an 80Ah pack that could take a very long time, so when the imbalance is severe it's easier to manually bring the low group(s) up with a single cell charger of some sort.

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Thanks for the reply. This gives me hope I can revive it.

I'm a complete newbie with this. Could you elaborate on what you mean by "[the BMS] tries to drain down that full group to allow charging to continue on the remainder. On an 80Ah pack that could take a very long time, so when the imbalance is severe it's easier to manually bring the low group(s) up with a single cell charger of some sort."

The battery in question is a block with the blue shrink wrapping. I've never tried to take one of these apart.

strip it down.
measure voltage on each cell and report back.
if you dont have a controlled power supply or charger capable of charging a single cell: get one.

flippy said:

strip it down.
measure voltage on each cell and report back.
if you dont have a controlled power supply or charger capable of charging a single cell: get one.

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Something like this?
Charger

Maybe something more like this

https://www.ev-power.eu/Chargers-6V-to-36V/Charger-3-6V-20A-for-LiFePO4-cells-1-cell.html

You can probably find a much better deal, and you might not necessarily need 20 amps, but you are dealing with very large cells that will take a little charger like the one you linked to a very long time to charge.

Important when looking for a charger for this job is that it supports LiFePo4 chemistry, it should terminate at 3.6V. A Li-Ion charger will go to 4.2V and that's too high for your cells.

dustNbone said:

Maybe something more like this

https://www.ev-power.eu/Chargers-6V-to-36V/Charger-3-6V-20A-for-LiFePO4-cells-1-cell.html

You can probably find a much better deal, and you might not necessarily need 20 amps, but you are dealing with very large cells that will take a little charger like the one you linked to a very long time to charge.

Important when looking for a charger for this job is that it supports LiFePo4 chemistry, it should terminate at 3.6V. A Li-Ion charger will go to 4.2V and that's too high for your cells.

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Alright thanks. Now I know what to look for. But how do you charge a single cell with those alligator clips? I would have thought the charger needed a housing of some kind to put the battery in.

No, stop thinking in double A cells and start thinking industrial.

Grab a nice new stanley blade and start removing foil. Dont stop until you hit the cells. I expect the connextions between the cells to have bolts. Remove them. Strip the pack further until you are left with 4 separate cells. You want this in order to separate them in one does decide to go thermal.

Thenthe first rule of dealing with cells: thou shall measure voltages.

If you have time then get a lab bench power supply. They are cheap and usually do about 5A. Not much but enough to get this party started and is not a one trick pony like the above mentioned charger.
First balance the cells out.

Report your voltages and i will give you a plan to get them up to snuff as fast as possible with a bench power supply.

It really depends how the battery is built. If you could post a picture of the pack we could probably suggest an easy way to access the connections to the individual cell groups. They're all going to be wired to the BMS board, so that's one option that usually minimizes the amount of disassembly required.

The alligator clips might not be what you end up using to make the connection, but again depends on the construction of the pack.

Here's the pack. It came with a 10A charger.

Alright, I stripped the pack down. There are 4 blocks, each with 4 packs of cells. I measured each individual pack. All the packs in one block measured the same.
In the picture below:
Top Left - 3.36v
Top Right - 3.48v
Bottom Left - 3.32v
Bottom Right - 3.15v

Now we're talkin' So you've got a pretty wide range of charge states there, though it might not seem like it. Average voltage for LiFePo4 is about 3.2V, full charge is 3.6 and 2.8 or so is quite dead. So you've got one group that's near full at 3.48, and one that's less than half full at 3.15.

The BMS certainly had it's work cut out for it getting that back in balance.

Easiest thing to do at this point in my opinion is to charge each group up individually to 3.6V, you can reconnect the 4 cells from each group in parallel and charge them as a unit. Keep an eye on them during charging, mostly looking for heat and possible swelling of the cell cases. They look perfectly square from the picture, that's a good sign.

The fact that they got so far out of balance is a potential concern, but the chemistry itself is fairly safe as far as random self combustion goes. Hopefully a proper balancing solves it.

dustNbone said:

The fact that they got so far out of balance is a potential concern, but the chemistry itself is fairly safe as far as random self combustion goes. Hopefully a proper balancing solves it.

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I didn't mention earlier that I was basically given this battery by a friend and he said the battery had been sitting for 5 months. With that amount of time I'm not super surprised at the unbalanced state of charge.

I also wondered if the BMS might be failing in some way.

I haven't been able to find an adjustable power supply locally, so I'll need to order one from somewhere.

you can "donate" a usb charger in the mean time.

just cut a usb cable, make sure the polarity is right and hook it up to the lowest block. do connect ALL the same cells in that block together as i see that all the cells are disconnected. keep the cells of blocks connected.

leave it running for 2~4 hours until the voltage matches the next lowest block and connect that one up as well. continue this until you connected all 4 blocks as one big one running at 3.65v.

When charging never over charge so it takes a long time to get to 3.4 volt and after 3.45v it will race of to 3.6v. Don't go over 3.6v if at 3.45v don't walk away . It will overcharge very fast after that. When using those little Chargers check the charger do not just read what's on the side because what's written on the side does not match the output voltage of the charger you must check check for positive and negative before hooking up

What these battery for ? 12v 80ah. Could be a 48v 20ah bike battery or a. 3.4v 320ah battery flashlight battery.

flippy said:

you can "donate" a usb charger in the mean time.

just cut a usb cable, make sure the polarity is right and hook it up to the lowest block. do connect ALL the same cells in that block together as i see that all the cells are disconnected. keep the cells of blocks connected.

leave it running for 2~4 hours until the voltage matches the next lowest block and connect that one up as well. continue this until you connected all 4 blocks as one big one running at 3.65v.

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Nice! So charging with a 5v USB charger is OK (until it reaches 3.65)?
Seems like that might take a long time for an 80ah pack.

999zip999 said:

What these battery for ? 12v 80ah. Could be a 48v 20ah bike battery or a. 3.4v 320ah battery flashlight battery.

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It's a 12v 80ah battery for telescope and camera equipment. My setup draws about 4.5A per hour.

joelshort said:

Nice! So charging with a 5v USB charger is OK (until it reaches 3.65)?
Seems like that might take a long time for an 80ah pack.

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yes it will but its free and as it goes slow you have a low risk of frocking anything up. i doubt it will ever overcharge with that size battery.

joelshort said:

It's a 12v 80ah battery for telescope and camera equipment. My setup draws about 4.5A per hour.

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What kind of setup? Sounds big and automated.

amberwolf said:

joelshort said:

It's a 12v 80ah battery for telescope and camera equipment. My setup draws about 4.5A per hour.

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What kind of setup? Sounds big and automated.

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Yes, it's all automated.
http://buckeyestargazer.net/Pages/Equipment.php
I have 2 telescopes, one mount, 2 cameras, and support equipment. I'll be taking this equipment on an RV trip to some of the darkest skies in the USA. I need a Lifepo4 battery because they have a lot of capacity, are safer than other chemistries and can be charged quicker.

flippy said:

you can "donate" a usb charger in the mean time.

just cut a usb cable, make sure the polarity is right and hook it up to the lowest block. do connect ALL the same cells in that block together as i see that all the cells are disconnected. keep the cells of blocks connected.

leave it running for 2~4 hours until the voltage matches the next lowest block and connect that one up as well. continue this until you connected all 4 blocks as one big one running at 3.65v.

Click to expand...

Alright, I have an old 5v 3.5A USB charger. I hooked it up to the lowest voltage battery block. It started at 3.14v and after about 3 hours it got up to 3.22v. But it has stopped charging at 3.22v. I have left the charger on for an additional 4 hours and the block has remained at 3.22v

So what do I try next?

3.2v is where most of the charge is, so it will take a looong time to bring that up. If it's really putting out 3.5A, then since that block was less than half full, it would probably need 10+ hours to get past 3.2v. Keep an eye on it and leave it charging, then continue as suggested by Flippy.

amberwolf said:

3.2v is where most of the charge is, so it will take a looong time to bring that up. If it's really putting out 3.5A, then since that block was less than half full, it would probably need 10+ hours to get past 3.2v.

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Alright, thanks. I'll leave it on all day and see what happens. I was just afraid that if there was a problem with the block it would go nuclear if I left the charger on too long.

Oh, it could, if you left it on there till it overcharged...that's why you have to keep an eye on it the whole time.

If you had a 3.6v power supply it'd be safe enough to just leave it on there "unattended" for a few hours, but a 5V supply could seriously overcharge the cells it's attached to if not monitored and removed as soon as it gets to the point you need it at.

I doubt there's any problem with teh block other than it's cells ahve different internal resistance/capacity than the other blocks still at a higher voltage. (so it's capacity is the maximum capacity of the entire pack, which is likely noticeably, potentially significantly, less than the 80Ah it's rated for because of those cells).

joelshort said:

Yes, it's all automated.
http://buckeyestargazer.net/Pages/Equipment.php
I have 2 telescopes, one mount, 2 cameras, and support equipment. I'll be taking this equipment on an RV trip to some of the darkest skies in the USA. I need a Lifepo4 battery because they have a lot of capacity, are safer than other chemistries and can be charged quicker.

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Have to admit to some equipment envy; those are some nice pictures.

I just have a cheap 4" reflector found at Goodwill (with a broken automated mount; presently using a different tripod now that's equatorial instead, but all manual and very cheaply made, also from Goodwill), and eyepieces from an even cheaper refractor and other assorted unknown sources. Works ok for the bright stuff you can see in the city anyway, but given it's just a wish-I-could-go-there-instead-of-just-looking hobby, I can't spend the kind of money you have on yours.


Regarding the battery itself, none of the below really matters because you already have a battery taht works, but if you ever go to replace it:


There are other "safe" chemistries that can be charged even faster, like LTO (lithium titanate), and some of the various LiCo, LiMn, NMC, etc types can be charged quickly (though safety would depend on brand/quality, some are a lot better than others).

I use "safe" in quotes because for the same quality-level, LiFePO4 isn't necessarily any safer than any-other-chemistry, because QC is a big part of safety, and the cheaper it is the less QC there is, and the less consistent the resulting product is, etc. It's part of why cells that started out all at the same charge level end up greatly imbalanced as they discharge, because they have different internal resistances from each other (they shouldn't), and different capacities at the same discharge and charge rates.

I'd have to say that other than buying new first-level-quality cells from known-good-QC manufacturers (different from sellers/vendors, because you can get "seconds" from a lot of them without even knowing it; at least the manufacturers usually say which they are and sell seconds cheaper), the best place I've seen (based on stuff here on the forum and some of my own experiences) to get "matched" cells is from "totalled" EVs, or otherwise from EV packs. Since the BMSs in those EVs generally are not going to allow the EV to overcharge or overdischarge the cells, and even not let them outside a very narrow range of SoC, the cells dont' really get run very hard, relative to what they *could* do, and so they're usually still very good cells by the time they're scrapped out. As long as you can use them in some of the "blocks" they already come in, they can be really easy to use, and can be easy enough to use in smaller sections if necessary (like for lower-voltage packs like yours), and just parallel them for greater capacities.