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I have disassembled a battery pack for an old (2007-ish) Panasonic camcorder. The battery pack would not charge, so in the interest of pyromania science, I decided to try to learn what's up.

The two batteries from the pack are labelled CGR17360 Li-ion MH12210. I have found http://www.datasheetcafe.com/cgr17360-datasheet-lithium-ion-battery which seems to match.

I measured one of the batteries and it was stable at 2.90v. The other battery was measured at -1.20v, a negative voltage. I verified the label was applied correctly, and I verified I was using the meter correctly.

So the question is: What is going on here? Is there any hope of reviving the second battery?

Does anyone have any experience using these batteries specifically in their projects? If so, anything I should know before going in?

Hints for any of these would be appreciated.

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  • \$\begingroup\$ are the cells separate or are they still assembled into a battery? \$\endgroup\$
    – jsotola
    Jan 2, 2018 at 3:21
  • \$\begingroup\$ They are separate. \$\endgroup\$ Jan 2, 2018 at 3:30

2 Answers 2

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The battery cells most likely differed in capacity and were discharged to the point where one cell was completely discharged while the other still had some emf left. This results in the discharged battery being charged in reverse and is called cell reversal. It can result in a negative voltage on the lower capacity cell. A quote from wikepedia:

Generally, pushing current through a discharged cell in this way causes undesirable and irreversible chemical reactions to occur, resulting in permanent damage to the cell. Cell reversal can occur under a number of circumstances, the two most common being:

When a battery or cell is connected to a charging circuit the wrong way around.

When a battery made of several cells connected in series is deeply discharged.

In the latter case, the problem occurs due to the different cells in a battery having slightly different capacities. When one cell reaches discharge level ahead of the rest, the remaining cells will force the current through the discharged cell.

This stack exchange post discusses the same phenomenon.

The battery is most likely irreversibly damaged.

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The accepted wisdom I have encoutered is that discharge of a "Lithium Polymer" cell below 2.5V causes irreversible damage. Discharge should be stopped at 3.0V. Reverse charging is certainly terminal, though to get as far as -1.2V with only two series cells suggests that something else is going on. I have just done the same as you (CGR-S006A camera battery, two series CGR17360 cells), and found that one cell, initially at 3.0V, would accept a full charge and deliver a healthy current; the other, at -.24V, is on its way to recycling.

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