48v 25ah Lifepo4 battery state of charge when shipped

Batteries, Chargers, and Battery Management Systems.
GT877   1 mW

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Joined: May 23 2016 7:19am

48v 25ah Lifepo4 battery state of charge when shipped

Hi I am very new to electronics so please forgive me if my question seems silly.

I recently purchaed a 48v 25ah Lifepo4 battery from Aliexpress.
Once I received the battery I first tested the voltage with a multimeter and it was exactly 49v which I understand is normal as they are always sent partially charged.
I wanted to know however what 49V represents in state of charge %

Using a plug in watt meter I connected the battery to the charger that was supplied with the battery which is rated at 54.75V at 5A and also selecting the KWh mode to see how many watts will be used to charge up the battery.
After 2 hours & 30 minutes it finished charging and on the KWh display it showed 0.728.
Does this mean it consumed a total of 728 watts over the 2 hours and 30 minutes or it consumed 728 watts per hour making it around 1820W?
That would seem unlikely as 48v x 25ah = 1200W
and for the charger output, 54.75V x 5A = 273.75W
and 273.75 x 2.5 (2hr 30m) = 684.375W

The reason I am asking all of this is because I want to be sure the battery is not falsely advertised as 25ah when it may be lower so if anyone knows what 49V would equal to in % of charge.
If 49V is divided by 16 cell packs that would make each cell pack around 3.0625V

The battery cells are: 3.2v 3C 26650 cell
The BMS is contained inside the battery so I cannot access it without taking it apart.

I have not connected the battery to the controller yet.
I understand you are not supposed to run the battery empty especially at the start during the break in period so I would rather not do this yet to gauge it's full capacity.

I tried looking around for a clear answer to my question but I also wanted to elaborate a bit more.
Thank you so much for taking the time to read this and sorry if it seems like an odd question!

dustNbone   10 kW

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Location: Vancouver, BC

Re: 48v 25ah Lifepo4 battery state of charge when shipped

49V on a 16S LiFePo4 pack is about 50% charged.

You measured about 728Wh going in, but you have to subtract about 15% to compensate for inefficiency of the charger itself, so probably just over 600Wh went in. If you calculate 48V x 25Ah you get 1200Wh total capacity for the battery, so you're right in the ballpark.

Running a LiFePo4 down to cutoff on occasion isn't necessarily going to harm it, leaving it there for an extended time will however. So if you do, just make sure you charge it back up ASAP.

The opposite is also true, you want to avoid storing it fully charged for extended periods.

john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

54.75V is a great Absorb / CV voltage for 16S LFP.

If it uses that as a stop voltage, CC-only, the bank will be 5% or more below its theoretical top capacity.

Which is fine, pushing much higher could be stressful to longevity.

Holding that voltage until the charge rate falls to 1-2A would make a good "100% Full benchmark" for say, capacity testing or top balancing.

Be sure to balance your cells properly before putting into use.

Do not let them get too deeply discharged either, stop long before the weakest cell hits 3.2V at high discharge rates, use 3.3V otherwise.

dustNbone   10 kW

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Location: Vancouver, BC

Re: 48v 25ah Lifepo4 battery state of charge when shipped

john61ct wrote:
Nov 17 2019 3:16pm
Do not let them get too deeply discharged either, stop long before the weakest cell hits 3.2V at high discharge rates, use 3.3V otherwise.
That's literally where my LiFePo4 spends almost it's entire discharge cycle. If I stopped when I was hitting 3.2V per cell under load I'd be using like 1/4 of the capacity. Even at 3V per cell it's still got well over 25% left. And that's on a seriously understressed pack. Recommended cutoff is 2.5V.

GT877   1 mW

Posts: 16
Joined: May 23 2016 7:19am

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Great! Thank you so much for your reply. That has put my mind at ease then as I was completely unsure on the charge state and this makes perfect sense that it was charged by around 600w.
I would love to see a chart showing the voltage correspondence to state of charge for quick reference if that is something that exists.

I admit it is strange that the BMS cannot be accessed but according to the seller this BMS is capable of automatically balancing the cells.
So is it true that the cell packs discharge in unequal amounts by quite a contrast? Is that why you said you must stop when the weakest cell hits 3.2v? It is a shame I can't monitor the voltage of each cell pack but I suppose there is nothing stopping me from opening up the battery to access the BMS if I want to properly look after and monitor it.

Yes it also states the cutoff is 2.5v with this BMS and I agree I always thought 3.2v was the resting voltage with the widest state of charge thereby making it difficult to determine how much is precisely left in the battery but if 3v represents an amount between 25-50% then 3.2v must be well over that.

I will have to look around for a chart.

I will be connecting it all up tomorrow for it's first test.
Thanks again to both of you for answering quickly. I really appreciate it and will remember now that 50% is the charge amount a lifepo4 battery is shipped at.

john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

Yes, crossed wires with the other LI chemistries.

3.0-3.1V more like, very little usable capacity below that, and very stressful to longevity.

Actual cutoff will depend on C-rate.

GT877   1 mW

Posts: 16
Joined: May 23 2016 7:19am

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Thanks for clarifying. I do want to make sure that this time I properly look after this battery and make it last as long as possible as unfortunately I did quite the opposite with my previous battery!

john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

Checked last discharge cycle on a pack of 120Ah cells

DoD almost 90%, 107Ah removed

After resting a few hours, 3.22 Vpc

This is **much** lower than is healthy for longevity.

GT877   1 mW

Posts: 16
Joined: May 23 2016 7:19am

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Hi thanks for your message, what does DoD stand for?

I have a new concern now. I've checked the voltage after the battery has been fully charged and it reads 51.9v and soon went down to 51v
However the discharge cut off according to the seller's information is 54.75v
So what happens is once the charger fan turns off and while the charger is still connected to the charge port of the battery, using my multimeter the reading on the output wire reads 54.9v but once I disconnect the charger the reading jumps down to 51.9v and settles around 51v

Is this normal? Is the charger still charging even once the fan turns off?
What should a fully charged 48v LifePo4 battery read?
Can a BMS really auto balance all the cells? Is that what is currently happening?
At 51.9v each cell may be around 3.24v

SlowCo   100 kW

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Location: The Netherlands

Re: 48v 25ah Lifepo4 battery state of charge when shipped

If it is a 16S (16 cells in Series) LiFePo4 battery pack then a fully charged pack should be between 56V (3.5V per cell) and 57.6V (3.6V per cell). Max. 3.65V per cell = 58.4V should be the top resting voltage but is too high for a long life.
My 16S LiFePo4 pack has a BMS that balances the pouches at 3.5V each. The charger is set at 60V. I've done around 4000 miles with it in 1.5 years of use now. Still going strong.

john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

DoD = Depth of Discharge, inverse of SoC, so 60% SoC = 40% DoD.

john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

Please confirm this is 16S LFP chemistry.

If so then converting to per-cell voltages will make things easier.

54.75-54.9V is a near-perfect finish charging voltage, and yes LFP drops when charge removed.

But the immediate drop to 51.9V implies a load, bank not isolated, as does 51V. Or faulty cells.

You need to use an ammeter to see how much current is flowing and in which direction.

There are thousands of different BMS with different balance algorithms. Some require holding charge at too high a voltage, for too long, can be days, to finish balancing.

GT877   1 mW

Posts: 16
Joined: May 23 2016 7:19am

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Hi there I'm afraid I am unsure as to whether it is 16S but I imagine it is and it is sold as a LifePo4 battery and the cells are stated as 3.2v 3C 26650 cell.
The overall battery measures 80mmx200mmx330mm and weighs around 8.5kg.

That is interesting to read about a possible load inside the battery, I do have an ammeter but I always thought you had to place the ammeter between the battery and the load? I am sorry about my lack of knowledge but I will read into this to get a better understanding.

Unfortunately I cannot access the cell packs as of yet but I will try and get access to the BMS soon so I can see the voltage of each cell pack. I should have known if I read carefully that the BMS was integrated inside the pack. I am not sure why they have done this.
Is it possible that some sellers falsely advertise it as a LifePo4 when infact they could be sending a lithium ion instead? I think the size and weight however would suggest it is a LifePo4.

It is a shame that the seller does not respond at all to help clarify my concerns.
I still have the option to open a dispute for the time being which is why I wanted to be sure that everything was fine ASAP

This is some info copy and pasted from the page;

Battery Model: 4825
Voltage: 48V
Capacity: 25AH
Type: 3.2v 3C 26650 cell
Source Resistance: 40

Battery Quality
1. Cells - A grade cells to make sure batteries in high and full capacity
2. Protection - Dual IC chips, that can anti-short circuit, anti-over charger, anti-over current, anti-overload
3. Compose Type : Injection Technology to make battery more stable.
4. Certifications : CE,UL,FCC, RoHS, ISO9001
5. Long life cycle, No memory, environment friendly.

BMS informations
Our BMS consists of Master BMS Circuitry (we named “BMU”), Slave BMS Circuitry (we integrate it into our
battery module) and contactor. Besides the basic functions such as over charge/ discharge,over current, short
circuit, over temperature and balancing, Our BMS owns the following features,
1. Master-Slave architecture makes the system flexible;
2. Two level warning makes maintenance easier;
3. CAN2.0 and industrial level electronic components make system reliable;
4. Contactor makes high rate charge & discharge feasible;
5. Periodic insulation measurement makes personnel safety possible;
6. Host can control the system easily;

(I am not quite sure how the host can control the system easily if it's all sealed away)

999zip999   100 GW

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Location: Dana Point So. Cal

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Lifepo4 will settle to 3.5v per cell and 3.0v is as at the bottom. With new battery leave on the charger for many many hours after light turns red .Yes many hours for the bms to full up the low cell of a new battery . Yes the charger should turn off and on to full and balance the whole battery.. Make sure it's 16s . For 57.6v for charger and fresh off. The bms will bleed it down some or 3.5v per cell. Only use at rated watts. Good luck. My lifepo4 is 6.5 years old 1,420 charge cycles yea still runs strong A123 cells.

john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

LFP when Full will actually settle at 3.34-3.36Vpc once the "surface charge" is burnt off with a few mAh discharge.

I'm afraid you really do need to confirm what the pack is, if the seller is so horrible they won't tell you - also what cells were used - make sure to name & shame, really should avoid such idiots.

Might need to open the pack, Kapton tape, shrink wrap etc is NBD.

If 16S, 57.6V is a harmfully high maximum, unless at a high C-rate and CC-only.

Find out what the "start-balance setpoint" of the BMS is and sit just above that ideally until all the cells are within 0.01 of each other, as stated could be days with that usual very stupid algorithm most cheap BMS use.
Not what I said, I meant from outside

but yes, a bad cell broken BMS or bad wiring could do that.

> Is it possible that some sellers falsely advertise it as a LifePo4 when infact they could be sending a lithium ion instead?

Of course.

3. CAN2.0 and industrial level electronic components make system reliable;

6. Host can control the system easily;

These two are maybe "not as described". What selling market?

Really better off getting a pack custom made from a trusted vendor from your choice of cells, or DIY.

GT877   1 mW

Posts: 16
Joined: May 23 2016 7:19am

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Hi thank you again for the replies, I really do appreciate it.
I agree I could open a dispute for not as described and I am leaning towards doing this today as I believe my cover runs out in a few days.

I charged it for 12 hours over night and it read 51.5v (it seems to fluctuate between 51.9 and 51.5.
I decided to at least take a peek under the cover to see what it actually looks like. Here is a picture. (attached)
It looks like there are 8 cells in parallel (except for the 4 cells on the far right) and a total of 60 cells. There is only one layer it seems as the battery pack is very shallow at only 80mm.

Would anyone be able to tell me a bit more from what they can see on this picture alone? Everything looks good? These are LifePo4 cells? I've put the multimeter into the picture with the 2 prongs across 2 cell packs I believe in series.
I am not great at maths either but am I mistaken in thinking there are not 16 cell packs here?
I can't see clearly where the BMS is yet, the wiring and side panels are all hotglued together to the cell packs.

Since I have only opened one side cover panel of the battery here are the voltage readings across 2 cell packs each from left to right; 6.82 + 6.79 + 6.89 + 7.03 + 7.03 + 6.88 + 6.90 = 48.34
(I switched the correct polarity of the multimeter prongs compared to the example in the picture)
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john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

4P15S would make 60

With cells "rated" to charge up to 3.65V maybe, way higher than I'd want.

48V taken a bit too literally IMO, but. . .

The "resting after full" with a bit of surface charge left lines up then, take a few mAh off with a load they'll likely settle around 50V full, drop below 48V in use.

999zip999   100 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

But when 48v it will flatten out it's discharge compare to lii-on. What's your charger voltage ? 25ah. ?

john61ct   1.21 GW

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Joined: Dec 18 2018 2:06pm

Re: 48v 25ah Lifepo4 battery state of charge when shipped

From the OP
GT877 wrote: charger that was supplied with the battery which is rated at 54.75V at 5A

GT877   1 mW

Posts: 16
Joined: May 23 2016 7:19am

Re: 48v 25ah Lifepo4 battery state of charge when shipped

Ah ok thank you john61ct, I think I understand so it is essentially a cheap work around to selling a 48v battery.
Instead of 16s it is 15s so one cell pack less? So each cell pack is charged to it's very limit just to give it around the same reading as a healthy 16s pack. Would this imply the battery will not last as many years as its always being charged to the limit?

Another odd thing though maybe they are interchangeable is that the charger that was supplied with the battery is classed for a lithium ion battery and not a LifePo4.(See picture attached)

999zip999, what do you mean about the discharge? The charger is sold as 2A standard current and 5A max current.
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john61ct   1.21 GW

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Re: 48v 25ah Lifepo4 battery state of charge when shipped

No just that 48V is not precisely defined, just a label.

Volts are volts amps are amps, there is no LFP charger vs LI charger, just how they're set before shipping. Most vendors charge higher than many here think they should.

Best is to get an adjustable one.