DIY novelty fan conversion from AAA to Li battery mod

We got this fan as in a gift bag from a friend. The fan plays a cool ANZ ad, with blue LEDs and the persistence of vision effect.

As we are in a heatwave currently, I started using it get a fresh breeze at my desk -- another cool effect. And as it goes, eventually the battery started to run flat. What to do?

I have a handful of 3.7V 18650 Li batteries, so opted to adapt the fan to use one of the batteries. The voltage is a close match: 1x3.7V ~ 3x1.5V. After a bit of ripping of the plastic casing, and a handy rubber band I got what I wanted. The results aren't pretty but do the job, and the fresh breeze is back!