[BrianG]

Putting it in the freezer works too as it makes the epoxy more brittle. Just a gentle prying action breaks the connection quite easily. Whatever works...

Griffin, I realize that the cap could have had too much current, but wouldn't it have had to be multiple high current charges and discharges? All caps have the inrush of current on initial charge. From the looks of it, that cap is simply on the + and - inputs so it's not like there was an oscillator circuit on it to rapidly charge/discharge. Of course, this assumes that the batteries were connected right - which I'm sure they were otherwise there would be more issues that one cap I would think.

I still think there was something that caused this that isn't directly related to the cap, even though it looks like it suffered for it.

Are we all sure it is in fact a cap and not some sort of avalanche diode to shunt voltage spikes that are too high to ground. It does look like a cap though...