This one is great! It fully charges my phone at least like 3 times and its not that expensive

POWERADD 2nd Gen Pilot 2GS 10000mAh Power Bank, Dual USB Port Portable Charger 3.4A High-Speed Charge for iPhone, Samsung Galaxy, Other Smartphone and Tablet - Black (Apple Cable Not Included) https://www.amazon.com/dp/B00N2JBTEM/ref=cm_sw_r_cp_api_i_E8E3Cb574MHD9