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.
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.
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.
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.