Your 20,000mAh power bank is lying to you, but not how you think

Charge your phone from a brand-new 20,000mAh power bank and do the arithmetic. If your phone has a 5,000mAh battery, that brick should fill it four times. Instead, it manages two and a half, perhaps three, before giving up. It’s easy to blame cheap cells or an inflated marketplace listing, but a legitimate power bank may genuinely contain the advertised capacity.