It is awesome to see battery backup being added to the Pi. There aren't any good solutions currently short of a full on UPS or a consumer grade battery pack.
I plan on trying to use 2 in parallel to make a UPS for my pi.
I've used one with good results on a low power IoT door unlocker. When the door is closed, a Qi charger make contact and powers the device. When the door is open, it runs off battery.