12.8 lifepo4 batteries?

[Sadie04074]

Could someone please tell me what some lifepo4 "drop in" battery manufacturers mean when they call their batteries 12.8V batteries? I have seen this painted on the face of Power Queen, Chins, and other Chinese brands.

Lifepo4 batteries (12V) should charge with 14.6 volts and at rest should be about 13.2V, right? Some users on the WEB have mentioned that the 12.8V is a function of the BMSs "over current protection" and that with some chargers (like a WFCO auto identifying battery type converter) the battery reaches the over charge threshold every time it is charged and reverts to a12.8V reading when tested. However, in reality, the battery is actually fully charged to 13.2V at rest. Purportedly, after a small load is placed on the battery, the battery "wakes up" after a minute or so and reads the actual correct voltage?

Any help for my better understanding will be appreciated.

 

[Zapper77]

Could someone please tell me what some lifepo4 "drop in" battery manufacturers mean when they call their batteries 12.8V batteries? I have seen this painted on the face of Power Queen, Chins, and other Chinese brands.

Lifepo4 batteries (12V) should charge with 14.6 volts and at rest should be about 13.2V, right? Some users on the WEB have mentioned that the 12.8V is a function of the BMSs "over current protection" and that with some chargers (like a WFCO auto identifying battery type converter) the battery reaches the over charge threshold every time it is charged and reverts to a12.8V reading when tested. However, in reality, the battery is actually fully charged to 13.2V at rest. Purportedly, after a small load is placed on the battery, the battery "wakes up" after a minute or so and reads the actual correct voltage?

Any help for my better understanding will be appreciated.

Go off of the actual battery specifications, ignore the marketing.

 

[Zapper77]

If they said 14.6v battery, a large portion of the population would be confused.

 

[Sadie04074]

For example, here is one such battery:
https://www.amazon.com/LiFePO4-Rech...fos.f5122f16-c3e8-4386-bf32-63e904010ad0&th=1

12.8 voltage is only 17% SOC?

 

[Sadie04074]

If they said 14.6v battery, a large portion of the population would be confused.

I understand, but I am combining that with the fact that there are people on some RV sites who have purchased these batteries and are reporting doing full charges with their stock converters and only getting 12.8 volts. Others have responded by saying this is a product of faulty stock converters in RVs that supply too much charging or that over charging is taking place with the BMS responding accordingly. I decided to post here to get a higher level of expertise to explain this phenomena.

 

[Solarcabin Channel]

reporting doing full charges with their stock converters and only getting 12.8 volts

A standard non LFP charger will charge an LFP but it does not charge at the higher voltage an LFP needs so you will not get a full charge.

They make RV chargers for LFP batteries and older RVs should get one of those.

A 12.8 LFP is just a 12 volt battery to distinguish it from 24 or 48 volt batteries.

The difference is an LFP has twice the capacity of a flooded, AGM or Gel and will generally last twice as long.

LFP can't be charged below freezing so depends on the application as to which would be better.

 

[Supervstech]

All batteries have a resting voltage.

For SLA it is 12.6V
For LFP it is 12.8
For AGM it is 12.8

When calculating the Wh of a battery there needs to be a standard voltage you calculate from think of it as an average if you will...

LFP average voltage for calculating the Wh capacity is 12.8
So a 100Ah LFP is 12.8x100 or 1280Wh when drawn at a constant rare around .2C you should pull 1280Wh from a 100Ah LFP.

Any charging system has a range of voltage. With car starting batteries, you have the CCA and the alternator will operate the vehicle system anywhere from 13.1 to 14.5V

 

[KITROBASKIN]

I believe Supervstech is saying the resting voltage is determined after a full charge then the battery is allowed to just sit. Is it supposed to be left unused for how many hours?

 

[Supervstech]

I believe Supervstech is saying the resting voltage is determined after a full charge then the battery is allowed to just sit. Is it supposed to be left unused for how many hours?

No...
I am answering the question posted in the first post.

"What do they mean when they list a battery as 12.8V"

It is the average voltage the Wh figure is calculated from... (or the Ah figure off the Wh published figure.)

It doesn't mean the battery should output 12.8V
Because it can output anywhere from 14.8 to 10.0V

12.8 is the voltage mean.

 

[Sadie04074]

All batteries have a resting voltage.

For SLA it is 12.6V
For LFP it is 12.8
For AGM it is 12.8

When calculating the Wh of a battery there needs to be a standard voltage you calculate from think of it as an average if you will...

LFP average voltage for calculating the Wh capacity is 12.8
So a 100Ah LFP is 12.8x100 or 1280Wh when drawn at a constant rare around .2C you should pull 1280Wh from a 100Ah LFP.

Any charging system has a range of voltage. With car starting batteries, you have the CCA and the alternator will operate the vehicle system anywhere from 13.1 to 14.5V

Thank you, that makes sense. My point of confusion is the general discussions I have seen regarding the charging curve calling 13.2 or so as being the resting voltage of a lifepo4 battery after it being fully charged and sitting for some minimal length of time.

 

[mikefitz]

voltage.

For SLA it is 12.6V
For LFP it is 12.8
For AGM it is 12.8

Perhaps my batteries are different, but for a charged rested unloaded battery with surface charge disipated, I measure, plus/minus 0.1
volt,
SLA 12.7
LFP 13.4
AGM 12.9

So similar wilh lead battery readings but quite different with the LFP.

Mike

 

[OTRwSolar]

A standard non LFP charger will charge an LFP but it does not charge at the higher voltage an LFP needs so you will not get a full charge.

They make RV chargers for LFP batteries and older RVs should get one of those.

I've found old-school 3-stage 13.2v/13.6v/14.4v RV lead-cell converters charge 12v lifepo4's to 100% SOC just fine. No downsides. IMO, they're a better charging option than many so-called "Lithium Approved" single-stage (14.6v) and two-stage (13.6v/14.6v) converter/chargers---especially if you tend to use full hook-ups a lot. Much better to float a lifepo4 at 13.2v for weeks or months at a time than 14.6v which is what would occur if you used a Lithium Approved single-stage 14.6v converter.

The only caveat with the 3-stage lead-cell converters, make sure they don't have an equalization mode that exceeds 14.6v.

 

[Supervstech]

Oh no, LFP isn't supposed to read 12.8...

That is just the average voltage number that works out the math to calculate capacity...

Same as a LiNMC bank of 3 cells would be listed as 11.1 instead of the 12.6 it rests at...

Because Lithium has a sharp knee where voltage drops off... 13.2 is the outage it rests arlt the majority of the cycle... but the math doesn't work out there...