AnkerDirect via Amazon discounts a selection of external battery packs after coupon, as listed below. Prime members qualify for free shipping. (Non-members can spend over $35 for free shipping; otherwise, it adds around $6.) The deals, after coupon:

• Anker 2nd Gen Astro E4 2-Port 13,000mAh Portable External Battery for $23.99 via "ANKEREE4" ($6 low)
• Anker 2nd Gen Astro E5 2-Port 16,000mAh Portable External Battery for $29.99 via "ANKRPPE5" ($10 low)
• Anker Astro E6 3-Port 20,800mAh Portable External Battery for $42.49 via "ANKRCWE6" (pictured, $98 off)