The “internet of things” is great, in theory — the problem is that you need new connected stuff to replace your old unconnected stuff. Tethercell is trying to fix that: it’s basically a plastic sleeve that converts an AAA battery into an AA, grafting on Bluetooth 4.0 support that lets you control the flow of power with a smartphone. It can also send you alerts when you’re low on power, set on-off timers, and so on. In theory, it should work with any of the millions of gadgets out there that run on AA cells.
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.
I bet you could hack that battery holder and use it for something useful.