V5 Battery corrosion

I had a V5 battery die on us a couple days back. The battery would not charge and the red led was flashing when it was plugged in. A couple of days passed when my mentor noticed some dried up liquid around the 4 wire V5 battery port. He had us smell it and the port smelled sour like acid. We took it apart and I took the following images.
Here’s a view of the inside top connections for the 4 wire V5 battery port.

Here’s a picture of the contacts with the corrosion on the top of the PCB.

Finally a picture of the back of the PCB. You can see that the pins for the V5 battery port are corroded heavily on the back, as well as a number of other components.

My mentor thinks that one of the cells was defective and leaked acid, which resulted in the corrosion of the v5 battery port connection and the liquid around the port, as well as the sour smell.

I mean batteries go bad all the time due to hundreds of factors. It happens even in tesla…

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From some quick looking around on Wikipedia, I found that LiFePO4 batteries can use Lithium Percolate or Ethylene Carbonate (the latter of which is acidic maybe causing the smell) as electrolytes and are white solids at room temperature so that could be what the substance is.


Also, just out of curiosity, what kind of cells are in the battery?
Is it two 18650 size cells or four smaller cells?

four smaller cells.

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Thanks for the picture!

Thanks for providing tons of pictures, would you by chance be able to provide one more of the side of the cells? or is the black information on the side not 100% useful? I am curious to see who makes these cells and exact specs.

I’ll grab a picture tommorow. If I cut into the pink casing will I be hurt?

Probably these or very similar:


I think @vexvoltage wants to see the text that is printed on the pink casing. Usually nothing is printed directly on the metal that is behind the pink (in this case) casing.

Yes this is correct. @meepmeepme Please do not open the cells up. LiFePO4 can get unstable very fast and cause harm or damage.

What did the acid taste like?

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Nobody mentioned tasting the acid, just smelling it. However, to answer your question, humans perceive the taste of acids to be “sour” for example, citric acid in fruits, acetic acid (vinegar) in sweet-and-sour sauce, and phosphoric acid in cola beverages.

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It was a joke btw (20 chars)

I helps to add an emoticon to jokes :wink: and scarcasm :smirk: Otherwise, those of us who are concrete-minded engineers take everything way too seriously.


Just s safety precaution, but you should try not to smell strange substances unless you know what they are.

Have you called Vex about this yet?

There’s a pretty good chance of some not so nice things happening.

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Here’s the casing. Don’t worry, I learned my lesson about dangers of batteries when my mentor shorted the contacts on accident.
Here’s an image showing the surface of the PCB with bubbles. I didn’t notice this the first time around.

No, my mentor told me that we couldn’t RMA it cause if the cell was broken we can’t ship it.

What if you drove to the Vex robotics office? Is that far?