These are boost converters designed to boost low voltages to a stable 5V. I set them up with a pair of rechargeable AA batteries (2 x 1.2v = 2.4v) and a multimeter. Four boost converters produced a stable voltage of 4.88 to 4.94 volts. This is well within specification for the Arduino Nano and LED to work. They are pretty small. That's cool. I think a block is defective. It creates a connection but doesn't increase the tension; it does not "boost" and is therefore not suitable for this purpose. At this price I think that's normal.
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