A copper zinc gravity battery from start to end of usable life.

Any opinions?

Very cool man. Did you say it was about 3 volts?

Copper zinc gravity cells have an open circuit voltage of about 1 volt per cell.
This was a six cell battery, so OC voltage is about 6V
(6.4V to be exact)

The optimum load voltage is usually around 0.8V per cell
That would be 4.8V for this six cell battery.

They are relatively high resistance depending on the construction, so highly loaded they become more of a current source.

I had this one loaded down to 3V. (the voltage of the LED at that current)
Or about 0.5V per cell.(which is a pretty heavy loading)

But it was a relatively small battery so it didn’t produce that much current being that heavily loaded.
It produced around 40mA at that loading.
Shorted it produced around 60 to 70ma.

Optimum load current for this battery would be around 17 to 20mA.
Which would have resulted in a total voltage of about 4.8V or 0.8V per cell.

If I had tried that loading level with the larger cup sized cells that I had in the other videos, I would have melted the medium power LED.

If I had six of the larger cup sized cells lined up on that led it would have pulled over 200mA (0.2A) at the 0.5V per cell loading, and that LED is only rated at a design current of 100ma, and an absolute maximum of 200mA with a proper heat sink.