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Renogy 100ah LiFePO4 Battery voltage

seattleStu

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Oct 22, 2021
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I bought a new 100 ah Renogy LiFePO battery over the summer. It didn't hold a full voltage after being fully charged. I would charge it fully to 13.9 v. Then it would sit for a day with nothing connected to draw, and it would be 13.23 v after 24 hours. According to the Renogy chart, this was 75% or so of a charge. Chart attached for reference. After many weeks (8 weeks?), and hours on the phone, Renogy picked up the battery for testing. They determined there was a problem, and sent me another battery!!
I charged it up to 13.9 v using a Noco Genius 5 charger. Then a few hours later, it started dropping, and in 24 hours, with nothing connected, it was at 13.24. Now I am thinking that I am doing something wrong.
Is this another faulty battery?
Is my testing with a multimeter wrong or off?
Is there another way to test that the battery is full, not at 70 or 80% right away?
Thank you for any help, I know enough to be confused, but not enough to be confident!

dod-chart.jpg
 
Is there another way to test that the battery is full, not at 70 or 80% right away?
I would try charging it a little higher and see if that makes any difference. Is there a reason you picked 13.9V? What does your battery documentation recommend?

Or, if there is a way to absorb at 13.9V I would try that. I am not sure if the Norco just stops at 13.9V or ??

Just a thought.
 
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I would try charging it a little higher and see if that makes any difference. Is there a reason you picked 14.9V? What does your battery documentation recommend?

Or, if there is a way to absorb at 13.9V I would try that. I am not sure if the Norco just stops at 13.9V or ??

Just a thought.
The charger goes just above 14v, like 14.4 or so. But it soon drops lower.
 
How are you measuring voltage,? the meter may be slightly inaccurate.
Its normal for the voltage to fall on a resting battery, and will fall to around 13.4 volts. It will depend on temperature and the exact chemistry used in the battery.
The Noco Genius 5 charger is intended as a general purpose car battery charger and in my view is not optimal for a Lithium battery. Its advertised as suitable for lithium (if that mode is selected) charging to 14.6 volts, so I would expect to see the battery volts rise to near this voltage.
If you see the battery voltage rise above 14 volts you can consider the battery charged ( with a 5 A charge into a 100Ah battery).
You could measure the battery capacity. For a rough test apply a DC load that draws a known current, a car headlight bulb takes 4 amps. Measure how many hours it takes before the volts drop to 12.0 volts ( 10% capacity).
Each hour is 4Ah worth of capacity. Its not super accurate but will give you some idea on the battery performance.
( 90% of capacity should take almost 23 hours).

A more accurate test could be made with ,

DORK

Mike
 
How are you measuring voltage,? the meter may be slightly inaccurate.
Its normal for the voltage to fall on a resting battery, and will fall to around 13.4 volts. It will depend on temperature and the exact chemistry used in the battery.
The Noco Genius 5 charger is intended as a general purpose car battery charger and in my view is not optimal for a Lithium battery. Its advertised as suitable for lithium (if that mode is selected) charging to 14.6 volts, so I would expect to see the battery volts rise to near this voltage.
If you see the battery voltage rise above 14 volts you can consider the battery charged ( with a 5 A charge into a 100Ah battery).
You could measure the battery capacity. For a rough test apply a DC load that draws a known current, a car headlight bulb takes 4 amps. Measure how many hours it takes before the volts drop to 12.0 volts ( 10% capacity).
Each hour is 4Ah worth of capacity. Its not super accurate but will give you some idea on the battery performance.
( 90% of capacity should take almost 23 hours).

A more accurate test could be made with ,

DORK

Mike
Thank you! Here is my multimeter, it has been good so far.
1634943328050.png
Yes I have seen the Noco go above 14v, then rest, on Lithium battery mode.

thank you for the testing information.
 
That battery is fine. Put it in service. My LifePO4 all 3 of them settle to 13.4 -13.3 after charge. That's how they are.
 
I was in the same boat...Bought 3 of the Renogy 100ah self heating batteries. Started charging them to 14.4, float at 13.6, and after some hours of rest, they would all go downs to 13.3/13.2. They are in paralell.

I was trying to determine the same thing if they are defective or something was wrong, but I just got tired of doing tests and started to use them, so far they have held up pretty well.

The charts are indeed missleading and everywhere there are slight differences in voltages as to what % should be what voltage.

My last resort is now I have bought a battery capacity tester, and will test each battery individually, and if they all give full ah reading, I will settle down that these Renogy batteries are just what they are, resting at 13.3...
 
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