I Need advice on New TOPBAND 25ah cells from Battery Hookup.

[lonewolf754]

This is concerning a case of TOPBAND 25ah Lifepo4 New Cells purchased from Battery Hookup.
I'm still waiting for them to respond to my emails.

There is a voltage reading on some cells that the other cells Do Not Have.
I'm assuming one of these behaviors is normal and the other is a failing cell.

The voltages of the cells arrived with typical shipping voltages.

I check the voltage of the cell. Then, I remove the Neg lead from the cell and
place it anywhere on the metal casing of the cell.

Some of the cells show around 0.500v - 0.650v on their case.
While other cells have No voltage reading whatsoever on their case.

Are the cells that have a reading of voltage on their case, Bad?
Or, are the cells with a voltage reading on the casing the good ones?
Are they beginning to Internally Short? Dendrites?

Shouldn't all cells show or not show voltage on their casing?

I purchased these cells to make an E-bike 48v 25ah pack.

Thank you, I really need some advice.

 

[RCinFLA]

LFP metal case sealed cells are in contact with internal fluid electrolyte. A high impedance voltmeter will almost always show some voltage between either terminal and metal case. This is normal.

It will not support much load current, 20-50 microamps which is much less than normal cell self-discharge current.

You still want to avoid even 20-50 microamps by ensuring cell cases are electrically isolated. Any electrons flowing in electrolyte results in some breakdown decomposition of electrolyte.

 

[sunshine_eggo]

This is concerning a case of TOPBAND 25ah Lifepo4 New Cells purchased from Battery Hookup.
I'm still waiting for them to respond to my emails.

There is a voltage reading on some cells that the other cells Do Not Have.
I'm assuming one of these behaviors is normal and the other is a failing cell.

The voltages of the cells arrived with typical shipping voltages.

I check the voltage of the cell. Then, I remove the Neg lead from the cell and
place it anywhere on the metal casing of the cell.

Some of the cells show around 0.500v - 0.650v on their case.
While other cells have No voltage reading whatsoever on their case.

Are the cells that have a reading of voltage on their case, Bad?
Or, are the cells with a voltage reading on the casing the good ones?
Are they beginning to Internally Short? Dendrites?

Shouldn't all cells show or not show voltage on their casing?

I purchased these cells to make an E-bike 48v 25ah pack.

Thank you, I really need some advice.

I have a prior version of these same 3C cells when they were sold as Topband Navitas cells with green shrink. I just ordered four more to make an 8S battery. They just dropped the price right after I ordered at $14 to $12.50 each... WANT MORE.

I can confirm similar voltages on my cells.

This voltage condition between case and terminals is why folks often recommended additional separators between cells.

 

[lonewolf754]

LFP metal case sealed cells are in contact with internal fluid electrolyte. A high impedance voltmeter will almost always show some voltage between either terminal and metal case. This is normal.

It will not support much load current, 20-50 microamps which is much less than normal cell self-discharge current.

You still want to avoid even 20-50 microamps by ensuring cell cases are electrically isolated. Any electrons flowing in electrolyte results in some breakdown decomposition of electrolyte.

Thank you for responding. What about the cells that have no voltage measurement on their case, are they ok?

 

[lonewolf754]

I have a prior version of these same 3C cells when they were sold as Topband Navitas cells with green shrink. I just ordered four more to make an 8S battery. They just dropped the price right after I ordered at $14 to $12.50 each... WANT MORE.

I can confirm similar voltages on my cells.

This voltage condition between case and terminals is why folks often recommended additional separators between cells.

Thank you. I appreciate your response.

If the ones with the voltage on the case is normal, what about the ones without any reading on their case? That's what confuses me
because they don't all have that reading on their case.

 

[RCinFLA]

Thank you for responding. What about the cells that have no voltage measurement on their case, are they ok?

On a metal cased LFP battery it is possible but unlikely. Most have cell wrap open at the top to allow layer current collector terminals to easily escape from the wrap and inject electrolyte easily. Cells are assembled with pressure relief vent unplaced. They are placed in a vacuum chamber and electrolyte is injected. It is somewhat of a messy process with electrolyte flowing into wrap but usually some drips over the top edge and runs down the outside wrap plastic.

You can often hear some liquid electrolyte sloshing around at bottom of metal can from the overrun during electrolyte injection process.

The small amount of leakage current is flowing through the electrolyte that dripped over the edge making contact with metal case. Electrolyte is a hydrocarbon solvent with a little lithium salt dissolved in the solvent. It provides for lithium-ion migration transport within cell. It is just a conveyor belt for lithium-ion migrating between positive and negative electrodes of cell.

 

[lonewolf754]

On a metal cased LFP battery it is possible but unlikely. Most have cell wrap open at the top to allow layer current collector terminals to easily escape from the wrap and inject electrolyte easily. Cells are assembled with pressure relief vent unplaced. They are placed in a vacuum chamber and electrolyte is injected. It is somewhat of a messy process with electrolyte flowing into wrap but usually some drips over the top edge and runs down the outside wrap plastic.

You can often hear some liquid electrolyte sloshing around at bottom of metal can from the overrun during electrolyte injection process.

The small amount of leakage current is flowing through the electrolyte that dripped over the edge making contact with metal case. Electrolyte is a hydrocarbon solvent with a little lithium salt dissolved in the solvent. It provides for lithium-ion migration transport within cell. It is just a conveyor belt for lithium-ion migrating between positive and negative electrodes of cell.

View attachment 191548 View attachment 191549

Thank you for taking your time in explaining why there is a voltage on the case. If I understand correctly, the electrolyte that has spilled out
into the casing has created a pathway that connects it to the main battery enclosure, like an "extension cord", and that's why the Positive terminal and the case have a voltage reading.

So, the other cells with no voltage reading are Rare, but they are still ok? Sorry that I still have to ask but I'm still trying to fully understand
what you have explained here. I'll definitely do some research.

Thank you.

 

[sunshine_eggo]

I have a prior version of these same 3C cells when they were sold as Topband Navitas cells with green shrink. I just ordered four more to make an 8S battery. They just dropped the price right after I ordered at $14 to $12.50 each... WANT MORE.

Order received. I'm all-a-twitter to dig in...