I have three new lifepo4 100Ah batteries with bluetooth. After charging each separately to 100% state of charge and sitting for one week one battery is at 90%, another at 92%, and one at 98%. The two batteries at 90% - 92% arrived at my house new at 0% state of charge and the one battery at 98% arrived at my house new at 20% state of charge. I tested the capacity of each and they all were at 103Ah. Why would they have dropped so fast in a week? Should I do or check anything else, or is this normal?
Why would new lifepo4 batteries state-of-charge drop so fast within a week of sitting?
- Thread starter sdnomad
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Because they are junk batteries with high self-discharge?
or you are fooling yourself and not really getting them to 100% SOC
I'm going to go with junk batteries, no decent vendor selling good batteries delivers batteries with 0% SOC. Probably were at 0% SOC because of high self-discharge
400bird
Solar Wizard
The Bluetooth and BMS use energy even when sitting. That's one possible cause.
I found where it says LIFEPO4 batteries have a self-discharge rate of 5% per month. I would think they would have an even rate of discharge from the bluetooth and BMS and would expect 98% SOC after sitting one week like battery (3). But battery (1) and (2) have fallen 8-10% in one week of sitting disconnected. Battery (3) is the battery that arrived new at 20% SOC. Battery (1) and (2) arrived new at 0% SOC.
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400bird
Solar Wizard
I'm not saying Bluetooth is the only possibility just one that is overlooked.
A BMS calculates SOC by monitoring current on or out of the battery (must flow through the BMS).
Any internal self discharge in the cells will not change the SOC displayed by the BMS.
Maybe the BMS on your two that arrived at 0% and discharged to 90% is in a different mode, software or hardware revision, etc; something that uses more energy.
A BMS calculates SOC by monitoring current on or out of the battery (must flow through the BMS).
Any internal self discharge in the cells will not change the SOC displayed by the BMS.
Maybe the BMS on your two that arrived at 0% and discharged to 90% is in a different mode, software or hardware revision, etc; something that uses more energy.
MurphyGuy
It just needs a bigger hammer
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- May 20, 2020
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Not 100 amp hours.
400bird
Solar Wizard
He lost 10% in a week. That's not great, but it's 10ah, not 100
A week is 168 hours.
10ah/168 amps = 0.06 amps continuous
0.06 amps x 12 volts = 0.7 watts
I'm no Bluetooth expert, but that seems pretty low energy use for a module searching for a Bluetooth connection.
No arguments from me there, it's quite possible.
They shouldn't have delivered at 0%
The SOC is part of the information displayed in the battery's bluetooth app.
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The only thing that makes me wonder what's up is that all 3 were charged to 100% SOC according to the Bluetooth display, with a 3 bank lithium charger and all three have sat for the same length of time disconnected from anything. The bms on each battery stopped the charge at 100%. And now one is at 98%, one is at 92% and one is at 90%. They are all the same make and model batteries.
If the standard is 5% discharge loss over a month, then 8-10% in a week is on pace to be 32-40% discharge loss over a month.
400bird
Solar Wizard
Self discharge is internal to the battery, no current flows through the BMS so the SOC won't change to show the cells self discharging. Unless the BMS manufacturer went all out and included it in the algorithm.
But the BMS is constantly sensing the voltage on each cell and its SOC and displays that info in the BT app. It's only because the batteries are equipped with bluetooth that I can see the SOC at any given time. With my limited knowledge, I would think the BMS (BT or not) would always have to know the SOC of each cell or how would it know to disconnect when it reaches its low voltage cut-out limit?
400bird
Solar Wizard
Again, the SOC is calculated by coulomb counting. Basically, measuring the current flowing in/out of the battery. Cell voltage isn't used for SOC, other than to rest/correct it.
The cell charges up to 3.65 volts to reach 100%
It then relaxes down to something like 3.4 volts while still at 100%
If the BMS uses cell voltage for SOC, this would be difficult to compensate for.
Also, SOC goes from about 20% at 3.2 volts to 80% at 3.35 volts. The small voltage differential for the large 80% means cell voltage isn't usable to track SOC
The cell charges up to 3.65 volts to reach 100%
It then relaxes down to something like 3.4 volts while still at 100%
If the BMS uses cell voltage for SOC, this would be difficult to compensate for.
Also, SOC goes from about 20% at 3.2 volts to 80% at 3.35 volts. The small voltage differential for the large 80% means cell voltage isn't usable to track SOC
Do you care to share more info on the batteries you bought? I mean without naming the brand, where did you buy them? Let's say it's a popular brand like Battleborn or SOK, but you bought them from seller "gud-batteries-4u" on ebay (I made that user id up), instead of the manufacturer directly or a known reliable retailer, then perhaps you bought fake batteries or damaged/used ones. Did you buy from a reputable retailer/seller or from a no-name source? What is your warranty recourse should you discover these really aren't as they were advertised?
I'm no lithium expert but I know that no reputable seller would send you any kind of lithium battery at a 0% SOC. 80% is typical, but as low as 20% is fine. 0% isn't going to kill a battery overnight, but if it was stored that way for a long time, no bueno and could simply be a sign of battery with some damage to it, such as high internal resistance.
I'm no lithium expert but I know that no reputable seller would send you any kind of lithium battery at a 0% SOC. 80% is typical, but as low as 20% is fine. 0% isn't going to kill a battery overnight, but if it was stored that way for a long time, no bueno and could simply be a sign of battery with some damage to it, such as high internal resistance.
You've indicated you have the capability of capacity testing them. You have not indicated exactly what battery you are using.
Now test the accuracy of your bms and "soc" readings again, by doing your own capacity test as you did before after a full charge and letting them sit for a week.
It may also be true that a single charge/discharge cycle is not enough time for the bms bleeder resistors to attempt some sort of balance.
Do your own capacity test as you've done before to flesh out some of these variables which may be misleading.
Now test the accuracy of your bms and "soc" readings again, by doing your own capacity test as you did before after a full charge and letting them sit for a week.
It may also be true that a single charge/discharge cycle is not enough time for the bms bleeder resistors to attempt some sort of balance.
Do your own capacity test as you've done before to flesh out some of these variables which may be misleading.
Rocksnsalt
Solar Enthusiast
This is a bit different than the title says.
I have a Vestwoods Ultra 250ah 12v battery I use steadily this time of year in my Sprinter to run a maxxair fan, charge phone/ipad, and run a 12v 50L fridge when it’s needed.
Yeah I know it’s not a Victron, Lithionics, or even a Battleborn, Epoch, or Litime.
It holds charge fine for weeks when not being used much.
I’ve noticed a few times I may start at say 95% soc (per it’s crappy bt) run fan and fridge (normal cycling) for 2.5 days and the battery bt will show 84% soc. About 24hrs later I check the bt and the battery is down to 20%.
This has happened a few times when not using any external charging and ambient temp is relatively the same 65-80F - so it’s not the fridge working harder.
It’s like the soc just collapses.
Other than answers like “it’s a junk battery” etc, what causes soc to be looking normal/acceptable then basically collapse in a short time?
Cells out of balance? They were never perfect. The ability to observe cell balancing disappeared after a bt app “update.”
Looking for constructive answers please.
I have a Vestwoods Ultra 250ah 12v battery I use steadily this time of year in my Sprinter to run a maxxair fan, charge phone/ipad, and run a 12v 50L fridge when it’s needed.
Yeah I know it’s not a Victron, Lithionics, or even a Battleborn, Epoch, or Litime.
It holds charge fine for weeks when not being used much.
I’ve noticed a few times I may start at say 95% soc (per it’s crappy bt) run fan and fridge (normal cycling) for 2.5 days and the battery bt will show 84% soc. About 24hrs later I check the bt and the battery is down to 20%.
This has happened a few times when not using any external charging and ambient temp is relatively the same 65-80F - so it’s not the fridge working harder.
It’s like the soc just collapses.
Other than answers like “it’s a junk battery” etc, what causes soc to be looking normal/acceptable then basically collapse in a short time?
Cells out of balance? They were never perfect. The ability to observe cell balancing disappeared after a bt app “update.”
Looking for constructive answers please.
wheelman55
New Member
Try cycling the batteries several times. Run them down to 20%, then charge individually to 100%.
Might help. It’s important to charge them one at a time for these cycles.
Best of luck.
Might help. It’s important to charge them one at a time for these cycles.
Best of luck.
mikefitz
Solar Wizard
- Joined
- May 28, 2020
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- 3,161
It's very unlikely for the battery to loose that much power In a week, disconnected from everything. I suspect the BMS has not had enough charge/discharge cycles to accurately compute state of charge. It's possible for the voltage to fall slightly as the surface charge dissipates . What is the battery voltage showing on a votmeter?
Suijkerbuijk
I cannot be held responsible for this information.
Bms with bluetooth can use a lot
I had set my battery away with about 80% charge
After 6 Monts the battery is about 20% .
It can eat a lot .
Its a 150Ah battery
Wel my power pack with lipo4 still holds charger from 100% soc to 70% in the same time but do not have bluetooth option its a 30Ah pack.
So for the rest .
You can have graden c or lower cells.
You need to find out what for cells you have and look op.
I had set my battery away with about 80% charge
After 6 Monts the battery is about 20% .
It can eat a lot .
Its a 150Ah battery
Wel my power pack with lipo4 still holds charger from 100% soc to 70% in the same time but do not have bluetooth option its a 30Ah pack.
So for the rest .
You can have graden c or lower cells.
You need to find out what for cells you have and look op.
Rocksnsalt
Solar Enthusiast
I’m not sure the last 3 posts were responding to mine but if so, I have ONE battery, 250ah. It’s been cycled several times. The battery can sit for weeks and barely lose any state of charge, and actually has to be “awakened” some times.
And it doesn’t appear Vestwoods is a fly by night co
www.vestwoods.com
that would put grade C cells in a battery. At least imo and by appearance. They are not huge by any means but seem relatively legit, though their cs is not the greatest but heck that’s relatively common these days and this type of battery is likely small potatoes to them.
And it doesn’t appear Vestwoods is a fly by night co
Products
www.vestwoods.com
that would put grade C cells in a battery. At least imo and by appearance. They are not huge by any means but seem relatively legit, though their cs is not the greatest but heck that’s relatively common these days and this type of battery is likely small potatoes to them.
I’m not sure the last 3 posts were responding to mine but if so, I have ONE battery, 250ah. It’s been cycled several times. The battery can sit for weeks and barely lose any state of charge, and actually has to be “awakened” some times.
And it doesn’t appear Vestwoods is a fly by night co
Products
that would put grade C cells in a battery. At least imo and by appearance. They are not huge by any means but seem relatively legit, though their cs is not the greatest but heck that’s relatively common these days and this type of battery is likely small potatoes to them.
Bottom of the page on that site you linked to has this:
Looks like a Chinese company... so not sure that you can just assess as "not a fly by night company". There are lots of chinese companies that assemble batteries using cells from XYZ cell manufacturer and BMS from ZYX BMS manufacturer, with the case cut out at ABC Metalworks. Then after all assembly is completed either their own name or the name of some U.S. company gets slapped on and you end up with a cheap battery that will work, but if you happen to be a professional who works with quality batteries, you see how much better they could be. Some things are minor, others end up with battery failure in 3-5 years.
If your SOC% number drops like that, they may be simply using voltage to "guestimate" the SOC%. I have seen a number of batteries that have "SOC meters" on them that simply use battery volts as a rough reference to %. Usually with those, when you hit it with a big load the SOC% will drop and if you hit it with heavy charging the SOC% will jump...
What you could do as an analysis of the SOC% metering, is get a battery monitor from a reputable manufacturer (such as a Victron BMV-712 or SmartShunt) and track SOC% through that and compare. There is a good chance the meter on the battery will be way off as compared to a good 3rd party battery monitor.
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