I'm pleased with this cheap Suaoki K12's ability to jump start smaller cars and motorcycles.
I gave my last USB battery kit away, a young lady was needing her car jumpstarted an awful lot and seemed it seemed the nice thing to do, (and I didn't need all the laptop dongles that were included.) I decided to try this low-cost 8000mah replacement, and it works.
Suaoki K12 USB jumpstart battery via Amazon