Help putting together some off the shelf low voltage heating components

Hi everyone..

I'm looking to put together a small personal project and need help with the components.

Ideally, I'd need all the components to fit inside this box.

In an approximate 5" x 6" x 3" plastic box (2-3mm thick with no other insulation at this point) where the volume will be ~50% consumed by an existing object, I want to raise the internal air temperature from 72F to about 75F.

The heating element should cycle on / off as the temp reaches 75F max and 72 min.

This would be used 100% indoors and ambient (external to my enclosed box) temps would never dip below 60F while the heat box is in use.

I wanted to include a thermostat / controller / heating element / rechargeable battery pack inside the box. The size of the box can vary a little to accommodate all these components.

I was looking at using components such as these:

1. thermostat / controller
2. heating element

But I am confused if I can find a small enough battery to power these as they are 12V.

Should i be looking for lower voltage versions to accommodate a smaller USB C rechargeable battery? Are there similar components that operate on lower voltage?

Is there anything I'm missing?

thanks!