when idle, or just simply reading webpage/pdf, the 13' touch bar consumes ~5-8w of power.
typical battery packs NOT specially designed for usb-c has an output of ~10-12w, so it will change, just painfully slow. and the MacBook looses battery power whenever it encounters any demands (such as loading webpage, launching apps, editing... etc)
some battery pack designed for usb-c (I mostly see just chargers, not battery packs) may charge at up to 29-30w, so they will charge your MacBook, just much slower than the original charger.
that's all for 13 inch, 15 inch consumes a lot more power so...