Last year my boyfriend combined our external charges and our phones lasted till the last day. His charger was a solar one! and mine was this one highly recommend both!!!

That's why I snagged this in a $21 lightning deal on prime day! https://www.amazon.com/gp/product/B014GRM294/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1