I like to fish at night. So I built 3D printed bobbers with an LED diode and scavenged LiPo batteries from vapes inside. It has a dime sized wireless charger receiving coil that is glued inside to a slightly flattened bottom. Externally I built a mini solar panel that charges a scavenged 18650 that charges the battery with a wireless transmitter. The bobber is about the size of a golf ball. I used a slow blinking LED diode that changes color of the bobber. Haven't caught a fish with it yet but it is mesmerizing watching it change colors and bob on the water.