This pattern is a total stash buster, you don’t need much. I did use a sport weight yarn and smaller hook because that’s what I wanted to use up of my stash, but as long as both crocheted pieces measure 2cm wide after round 3, most battery pens should fit, the height is customizable. Just insert your pen as you go to see how tall it needs to be.

I have made a short chubby square battery holder and a 10cm tall slender pen holder. You can make each their own separate cap or use the cap for both bags.