Is this USB charger for powering your laptop? If so, why not use A123 cells? You could buy a 15Ah prismatic for $37 + shipping and that could go in your bag with a few heat shrink layers on it for protection, or even some stiff rigid plate for added security?
“The modern astrophysical concept that ascribes the sun’s energy to thermonuclear reactions deep in the solar interior is contradicted by nearly every observable aspect of the sun.” —Ralph E. Juergens