(Please go easy on me, I'm a hobbyist newbie.)
I'm taking apart a dollar store solar garden light for the sake of leaning. I've identified the parts in the very simple device--solar cell, on/off switch, white LED, resistor (so the LED doesn't get too much current), diode (so the power supply doesn't "backwash" into the solar cell, I imagine), and a capacitor to store the energy from the solar cell. I was surprised to see a capacitor rather than a rechargeable AA battery, but whatever.
But while there are markings on the resistor and there are markings on the diode, so I can look those up and know their stats, there are no markings on the capacitor, which surprised me. It is a cylinder about 1/4" in diameter and about 3/4" long. There is a positive lead to one end and a ground lead to the other. Near the positive end there's a dimple running around the circumference, but it's otherwise of uniform size up and down the cylinder. There is a yellow plastic covering over the cylinder, with no markings on it. The open ends of that cover show me a flat metal terminal at the ground end, and a smaller flat metal terminal in the middle half or so of the positive end, with a sort of "terra cotta" colour around that. That colour makes me wonder a little if it's not a ceramic capacitor, but aren't those always "flattish"--discs or squares or something--and cylinders like these are usually electrolytic, including that "dimple", the ring dent near one end, right?
As I type this, another thought occurs to me--is this perhaps just a less-standard-shape battery?
(If my descriptions are awful, I can add a photo later, it's just awkward from where I'm typing this right now.)
I put 3V through a 100 Ohm resistor and then across the LED to see if it would light, and it did, and then faded. I assumed it was charging the capacitor a bit, so did the same thing directly to the capacitor's terminals, and had the same result--the LED lit, and then when I removed the leads, it stayed on for a bit and faded out. It began to fade after about two or three times as long as I "charged" it (which was only about three seconds), and then faded down to a very dim glow which lasted for perhaps half an hour afterward (I'm still learning about my multimeter, but I know this component is putting out about 0.78VDC at this point).
Any thoughts on how I can identify this component? Is there a test I can do with my multimeter which will tell me more? First off, things I can try without removing it from the circuit it's in are best, as I hope to learn about it before I completely take it apart.