Huge lithium degradation

[91cavgt]

3 years ago I built a 300 amp/hr 12 volt battery using parts from Battery Hookup. I don’t remember what cells they were, but they were branded as Battery Hookup brand. Basically just a heat shrink cover over the cells. The batteries were cylindrical cells, already built into 100 amp/hr packs. 4 of these in series gave you your 12 volt battery. So, I bought 12 of these along with three 100 amp BMS. I wired them all up, as 3 individual 100 amp/hr batteries, each one fused with a 125 amp fuse, then mounted them all inside a wooden box with each individual battery connection being in the side of the box so I could hook them up separately, or all wired in parallel, on the outside of the box.

For 2 years, these were mounted in the basement of a 5th wheel RV. The converter on the RV had a switch to go from a traditional battery or a lithium battery, so it was switched to lithium. The battery was only used as a backup, and only was used a few hours during that 2 year period. We never boondocked in the RV, it was always connected to shore power, and we only moved the RV twice during this time period(we were full timing in it at that time).

1 1/2 years ago I took the battery out of the RV and put it in my shed to run my small work bench. It is recharged with three 250 watt 24 volt panels that are wired in series, then they are connected to an EPEver Tracer 10415 AN MPPT charge controller. The charge controller is rated at 150 volt input maximum and 100 amp maximum output.

I’ve got 2 power inverters connected to this setup (both 2,000 watt), a 1,000 watt car audio stereo system, and use the setup to recharge my Ryobi 18 volt and 40 volt batteries.

Over Christmas, I used this setup to power Christmas lights. The 2,000 watt power inverter I use the most is a pure sine wave inverter with a display that shows power output in watts. With all of the Christmas lights running, the display was showing 120 watts of output. With this load on the batteries, they only lasted for 6 hours before the power inverter shut off because of low voltage(it shuts down at 10.5 volts if I remember correctly). So, I removed lights and got the power output of the inverter down to 60 watts. At this level, the lights would stay on all night, but the battery was at a low voltage of around 12.3 volts in the morning.


That seems to be a rather large amount of degradation. I have disconnected the batteries from each other to confirm that there is power on each battery, so the fuses have not blown and each BMS is passing power. While the sun is out, the charge controller is set to charge the batteries to 14.6 volts, but as soon as the sun sets, the voltage drops down to 13.4 volts on each battery, and has done this since day 1. Were these just bad cells that I got?

 

[chrisski]

Hard to tell, but I’m betting on too high a charge voltage, or charging at freezing.

If your area of south Texas had the battery drop below freezing when charging either from solar or the lithium converter this could shorten life.

When the cells are charged to 14.6 after moved from the RV, this causes each cell to charge an average of 3.65, so it’s easy to overwork one cell with imbalancing. I charge my batteries at 3.45 per cell.

When in my fifth wheel, I store may batteries at 50% SOC with all loads removed. This is my best practice based off stuff I found on the forum here since the cells I made my batteries out of had no instructions. It is in storage at least 6 months a year.

Did the BMS’s have adjustable parameters?

How many cylindrical cells in each of these packs that you got from battery hookup?

Do you plan on any further action with this? Checking individual batteries to see if one is bad dragging the others down or even going to the cell packs and then the cells?

 

[42OhmsPA]

I remember seeing those packs.
I'm betting things are severely out of balance and degradation isn't that bad.
We need more data, pack voltages, cell voltages, charging data, etc.

 

[91cavgt]

Hard to tell, but I’m betting on too high a charge voltage, or charging at freezing.

If your area of south Texas had the battery drop below freezing when charging either from solar or the lithium converter this could shorten life.

When the cells are charged to 14.6 after moved from the RV, this causes each cell to charge an average of 3.65, so it’s easy to overwork one cell with imbalancing. I charge my batteries at 3.45 per cell.

When in my fifth wheel, I store may batteries at 50% SOC with all loads removed. This is my best practice based off stuff I found on the forum here since the cells I made my batteries out of had no instructions. It is in storage at least 6 months a year.

Did the BMS’s have adjustable parameters?

How many cylindrical cells in each of these packs that you got from battery hookup?

Do you plan on any further action with this? Checking individual batteries to see if one is bad dragging the others down or even going to the cell packs and then the cells?

The BMS units were pre-programmed and have no way to communicate with them.

There are 25 cylindrical cells per pack, all of which are connected in parallel. So each cell is rated at 4,000 mah. I know they aren’t 18650 cells. If I remember right, they start with a 3, but I don’t remember the rest, and the Wayback machine isn’t working for Battery Hook Up at this time so I have no way of looking up the info besides destructively tearing the battery apart, and I don’t want to do that.

Primarily, I’m just trying to make sure that I didn’t do anything wrong. Since the batteries dropped down to 13.4 volts once removed from a charge, I suspect something was not right with them from the get go. I’ve got 72 SPIM08HP cells that I made into a battery and they are doing great 4 years later, so I’m leaning towards just a bad batch of batteries.

I’ve not thought about testing each battery separately but that is something that I can do without taking the box apart that they are all in. I’ve got a little heater that pulls 250 watts. I guess I can charge all of the batteries up fully, then run the power inverter on each 100 amp/hr battery with the 250 watt heater to see how each one does.

 

[91cavgt]

I remember seeing those packs.
I'm betting things are severely out of balance and degradation isn't that bad.
We need more data, pack voltages, cell voltages, charging data, etc.

The only way I can get individual 100 amp/hr cell voltage is to take the box they are mounted in apart, which will take some time.

So would it be possible for all 3 BMS units to all allow an out of balance condition on each battery? The BMS units do not have any kind of communication so the only way to test them is to disassemble everything.

 

[42OhmsPA]

The only way I can get individual 100 amp/hr cell voltage is to take the box they are mounted in apart, which will take some time.

So would it be possible for all 3 BMS units to all allow an out of balance condition on each battery? The BMS units do not have any kind of communication so the only way to test them is to disassemble everything.

Do the BMS have communication so you can what individual cells are doing when you charge the batteries up to 14V?
What voltage were you charging them to?
It is possible for all 3 to be out of balance if they weren't charged full regularly.

 

[740GLE]

The BMS units were pre-programmed and have no way to communicate with them.

There are 25 cylindrical cells per pack, all of which are connected in parallel. So each cell is rated at 4,000 mah. I know they aren’t 18650 cells. If I remember right, they start with a 3, but I don’t remember the rest, and the Wayback machine isn’t working for Battery Hook Up at this time so I have no way of looking up the info besides destructively tearing the battery apart, and I don’t want to do that.

Primarily, I’m just trying to make sure that I didn’t do anything wrong. Since the batteries dropped down to 13.4 volts once removed from a charge, I suspect something was not right with them from the get go. I’ve got 72 SPIM08HP cells that I made into a battery and they are doing great 4 years later, so I’m leaning towards just a bad batch of batteries.

I’ve not thought about testing each battery separately but that is something that I can do without taking the box apart that they are all in. I’ve got a little heater that pulls 250 watts. I guess I can charge all of the batteries up fully, then run the power inverter on each 100 amp/hr battery with the 250 watt heater to see how each one does.

They are 32650 cells. If you do a search here you’ll find a fair about of others picked up these shrink wrapped “100ah kits”, some didn’t have good luck.

What BMS are you using, if you can’t tell the cell voltage you can’t tell if they are balanced. BMS have come a long way in 3 years.

 

[wpns]

You probably need to charge each battery separately with an adjustable supply to determine it’s disconnect voltage and see if it can be cycled or balanced back into proper operation.

If you can get at the cell voltage wires on the BMS with a DVM you can speed the process a lot.

 

[wpns]

So would it be possible for all 3 BMS units to all allow an out of balance condition on each battery?

Sure, why not? Each is independent, and any one battery can have problems with one or more cells. 3 batteries having problems simultaneously is unlikely, but one a year for the last 3 years is certainly possible, especially if they are not independent as they are built from the same lot of potentially dodgy cells.

 

[chrisski]

For 2 years, these were mounted in the basement of a 5th wheel RV. The converter on the RV had a switch to go from a traditional battery or a lithium battery, so it was switched to lithium. The battery was only used as a backup, and only was used a few hours during that 2 year period. We never boondocked in the RV, it was always connected to shore power, and we only moved the RV twice during this time period(we were full timing in it at that time).

the charge controller is set to charge the batteries to 14.6 volts,

The BMS units were pre-programmed and have no way to communicate with them.

Primarily, I’m just trying to make sure that I didn’t do anything wrong.

This probably could have helped:

1) Not charged the cells to the max lithium 3.65 per cell. Charging to 14.6 volts is 3.65 volts per cell.
2) Not kept the batteries at a full state of charge when not used for several years.
3) Not used a BMS with unknowns. No idea if that BMS is tuned to: 2.5 VDC min cell voltage, have cold/heat cutoff, have max cell voltage cutoff, balance, etc.

Any of the three above is what you could have done. With the BMS, if it doesn't control the parameters, the user needs to do that. Not easy. Many BMSs come with no temp sensor.

 

[91cavgt]

This probably could have helped:

1) Not charged the cells to the max lithium 3.65 per cell. Charging to 14.6 volts is 3.65 volts per cell.
2) Not kept the batteries at a full state of charge when not used for several years.
3) Not used a BMS with unknowns. No idea if that BMS is tuned to: 2.5 VDC min cell voltage, have cold/heat cutoff, have max cell voltage cutoff, balance, etc.

Any of the three above is what you could have done. With the BMS, if it doesn't control the parameters, the user needs to do that. Not easy. Many BMSs come with no temp sensor.

1. The pack has been charged to 14.6 volts.

2. The pack has never been in storage. It has always been connected to some kind of charger it’s entire life.

3. The BMSs that were used DEFINITELY seem to be suspect at this point.


I’m out of town right now so after I get back home I plan to individually test each pack with a 250 watt load and record the run time. I’ll then recharge the whole battery and disassemble the battery to test all cells. If the cells do show an imbalance then I guess the next step would be to get a charger that can charge the individual cells, and buy 3 new BMSs that have some way to monitor cell voltages. Lesson learned.

 

[FishHog]

They don’t do well being held at full charge. Sounds like you kept them there all the time so degradation is expected. These aren’t like lead acid batteries

 

[740GLE]

1. The pack has been charged to 14.6 volts.

2. The pack has never been in storage. It has always been connected to some kind of charger it’s entire life.

3. The BMSs that were used DEFINITELY seem to be suspect at this point.


I’m out of town right now so after I get back home I plan to individually test each pack with a 250 watt load and record the run time. I’ll then recharge the whole battery and disassemble the battery to test all cells. If the cells do show an imbalance then I guess the next step would be to get a charger that can charge the individual cells, and buy 3 new BMSs that have some way to monitor cell voltages. Lesson learned.

Best of luck. Be mindful there’s probably a reason why battery hookup doesn’t cary these kits anymore, and I don’t think it’s because they can’t get these cells anymore.

 

[91cavgt]

They don’t do well being held at full charge. Sounds like you kept them there all the time so degradation is expected. These aren’t like lead acid batteries

Well, their purpose was emergency backup power for when the power goes out while they were in the RV, and now they are being used as my primary power source for my off grid shed/work shop and they are setup right now as an emergency backup power source for my house. So keeping them at a lower state of charge would not be useful for my purpose. Should I have stuck with lead acid batteries??? I expect degradation to occur, but not to this extent with lithium in a little over 3 years.

I guess I have to see exactly what the cells are doing first before jumping to conclusions.

 

[FishHog]

Well you can store them at 60% charge and still have as much power available as fully charged lead batteries so not much difference. If you need more power then you need more batteries or deal with the degradation of keeping them full. Personally I’d split the difference and maybe keep them around 80% as most of the damage takes place at the high levels

 

[740GLE]

Well, their purpose was emergency backup power for when the power goes out while they were in the RV, and now they are being used as my primary power source for my off grid shed/work shop and they are setup right now as an emergency backup power source for my house. So keeping them at a lower state of charge would not be useful for my purpose. Should I have stuck with lead acid batteries??? I expect degradation to occur, but not to this extent with lithium in a little over 3 years.

I guess I have to see exactly what the cells are doing first before jumping to conclusions.

Did the chargers maintain a constant 14.6v or did they lower it to a more manageable 13.4?

Cause both voltages can be considered 100% full.

You can have 100% full batteries but at a much lower float voltage and not cause damage to the cells.

 

[91cavgt]

Did the chargers maintain a constant 14.6v or did they lower it to a more manageable 13.4?

Cause both voltages can be considered 100% full.

You can have 100% full batteries but at a much lower float voltage and not cause damage to the cells.

At night, the voltage would drop to 13.4 volts with no load on the batteries. During the day, Solar brings the voltage up to 14.6, then it lowers down to 14.1 volts. I assume that is the float voltage.

 

[Kornbread]

Well you can store them at 60% charge and still have as much power available as fully charged lead batteries so not much difference. If you need more power then you need more batteries or deal with the degradation of keeping them full. Personally I’d split the difference and maybe keep them around 80% as most of the damage takes place at the high levels

Well, there's this ...
" ... When you have a cell at 90% SOC for a prolonged duration, there will be a thickening of the SEI layer, and this will prevent some aging processes from occurring as fast. So the curve of degradation will actually flatten and over a few years, will be less than keeping your pack at 50%! That is crazy! ... ". from this thread https://diysolarforum.com/threads/c...4-batteries-used-for-solar-application.94487/

and this, " ... I think overall we will not be able to see cycling degradation in most solar batteries. It will be so minimal, that it will be hard to even measure. The calendar aging will be the majority of the capacity loss that you measure. ... ", from this thread https://diysolarforum.com/threads/c...imation-we-are-not-doing-100-dod-daily.98156/

If we take those studies at face value, it appears keeping LiFePo4 at a high state of charge may not hurt calendar ageing, which is the " ... majority of capacity loss ... ". The second study also extrapolates the major affect heat plays in LiFePo4 degradation.

 

[Vigo]

I think all the lessons that can be learned without looking at cell voltages have already been learned.. I would just try not to be overly pessimistic because there's still a good chance that a lot of the capacity is recoverable and its mostly down to imbalance, with a smaller amount of actual permanent capacity loss. Just gotta grind through the process of investigating. But as a fellow south texan ill be really interested to find out as the effect of the climate here is a real concern to me.

 

[FishHog]

Sure but seems like the op kept them at 100% all the time so I suspect he had some degradation. How much we don’t know and perhaps it’s an acceptable amount for him in his application

 

[91cavgt]

I’ve started checking each individual 100 amp/hr pack this morning. Got the solar disconnected from it and am running a 250 watt load right now. After this is done, maybe later this week or next week I’ll disassemble the battery box and test the voltage of each of the 12 cells.


I’m located south east of San Antonio where 100+ degree days are pretty common. I do have a temp sensor from the charge controller that is inside the battery so I can monitor battery temp. I’ve made sure it never got below freezing, but haven’t done much for the heat. The wooden enclosure these cells are in does have a small 40mm 12 volt fan in the bottom corner on one end. While in the RV, I connected a 2” PVC pipe to this fan, and ram the pipe over to a heated area of the RV basement. This kept the battery temp in the high 30’s when ambient temps dropped down to 12 degrees a couple of years ago. On the opposite top corner of the battery enclosure is a 2” outlet for the incoming air to escape. This 12 volt fan runs 100% of the time. The shed the battery is currently in is a 20’X20’ metal building that was built with bubble foil “insulation” on all sides and the roof. This, along with 2 windows that stay open during the summer months, keeps interior temps within a few degrees of ambient temps. In the winter time, when temps dip down really cold(for down here), I turn on a Little Buddy heater a few feet away from the battery and that prevents temps inside the shed from dropping below freezing.


I’m a novice at all of this, but I try to be somewhat informed.

 

[91cavgt]

The first battery test is now complete.

The battery started at 13.29 volts.

It lasted 2 hours, 48 minutes, and 50 seconds.

When the battery voltage hit 11.5 volts, the BMS low voltage was triggered and power output was disconnected.

This was with a 250 watt load according to the digital display on the 2,000 watt pure sine wave inverter. The 250 watt load was a small 120v personal heater.

 

[Vigo]

Was this just one of the 100ah packs? You got roughly ~75ah out of it AFTER the inverter losses, so maybe closer to 80ah? If that was out of a 100ah pack id say its a good sign, but if it was out of the whole 300ah id be vaguely alarmed.

I live right next to Calaveras Lake. Howdy neighbor

 

[91cavgt]

Was this just one of the 100ah packs? You got roughly ~75ah out of it AFTER the inverter losses, so maybe closer to 80ah? If that was out of a 100ah pack id say its a good sign, but if it was out of the whole 300ah id be vaguely alarmed.

I live right next to Calaveras Lake. Howdy neighbor

Yes, this was just one of the 100 amp/hr packs. It definitely lasted longer than I expected.

The second of the three 100 amp/hr packs is now being tested. I’ve got my Fluke multimeter connected to monitor the voltage, then a baby monitor focused on the Fluke that is powered by a Ryobi 18v small 150 watt power inverter. Inside the house, some 50’ away, I’ve got the display to the baby monitor. Now I can go about my normal daily activities while still monitoring what the battery is doing.


I’m south of Stockdale! It’s good to know there are some others around here!!

 

[42OhmsPA]

The battery started at 13.29 volts.

Was this the resting voltage?
What was the charge cutoff voltage?