The reason it's on a key is to protect your battery from being abused by charging phones, listening to the radio, and pumping up tires. Seriously, bike batteries are meant to start a bike and then be kept charged. The things you want to do are best done with a jump pack. I have and love this one:
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
This model is particularly good for people with USB-C devices. I can charge my laptop straight from it, and then charge IT from my laptop charger.