MOSFET Astable: NP-BX1 Rundown

After eight months from a full charge, an old NP-BX1 lithium battery has come to this:

The astable still ticks along at 1.4 seconds per blink, but the green LED barely lights up from a 2.1 V battery:

A pulse of 12 mV across the 100 Ω resistor puts the LED current at a mere 120 µA: no wonder the poor thing wasn’t visible in ordinary room light.

Another full charge restored its vigor for another couple of seasons.