A fully charged 6,700mAh portable battery can recharge an iPhone 7 battery (or similar phone) about 2 times.
The 12,000mAh has almost double the battery capacity and 2 USB ports for recharging 2 people's phones at once.
According to RavPower, these products include a 30 month warranty (2.5 years) when you register the product.
They also cover the shipping if the product needs replacement with 6 months.
We use a similar RavPower 10,400mAh and love it.
The charger is helpful when traveling and attending events outside of homes and offices where power outlets are not handy.
RavPower 10,400mAh Portable Battery Charger for $16 from Amazon with code RAV10400 .
Choose either Black or White.
We bring ours when out all day, to keep our devices charged when no USB/electrical outlet is handy.
This is especially helpful when flying on an airplane or attending a show/meeting/concert, where a phone running out of battery can cause problems.