I tested in 6 right now, and they all held more than 20 hours.
The effect is stunning in balloons, and as they weigh only 3 grams, you can even put them in balloons filled with helium.
ENVIRONMENT WARNING: these small LEDs are powered by 3 batteries! please do not disperse in nature, even if a drop of bright balloons can be very pretty.
Although it is not expected, these LEDs withstand prolonged immersion well (several hours), and I even frozen one in an attempt to create small bright icebergs.
The batteries are of a standard model, and can easily be replaced, unfortunately this is not necessarily economically profitable considering the price of the batteries.
Last precision: it shows in the pictures, the emitted light is white COLD.
Erwann on Amzon.fr