This 9v battery is dead and its ghost can power an LED.
@libc No, everything is way dumber.
I took the battery off infranted thermometer, checked voltage -- 2.7v. Then I attached a green led, which should be at 2.2v.
I connected the LED directly, no current limiting resistors, nothing at all.
The LED didn't blow. This battery is ded.
@avolkov As the surface area of the active metal is consumed the voltage remains the same but the current drops. Now, more power is being dissipated in the battery than in the LED.
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