Amazon has an Anker PowerCore Essential 20000mAh USB-C Battery Pack Sale, $34.99 after A1281369 and clipping the '$5 off coupon' -  Free Shipping. Expires Soon - Highly rated at 4.4 out of 5 stars.

• The Anker Advantage: Join the 50 million+ powered by our leading technology.
• Ultra-high capacity: The massive 20, 000mAh capacity provides more than 5 and a half charges for iPhone XS, more than 4 full charges for Samsung Galaxy S10, and over 2 and a half charges for iPad mini 5.
• High-speed charging: deliver an 18W high-speed charge to phones, Tablets, and more via the USB-C power delivery port or the Qualcomm Quick Charge-enabled USB port.
• Certified safe: Anker MultiProtect safety system ensures complete protection for you and your devices.

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