It doesn't matter what type of battery pack you get, as long as it has a USB connection. You can just use the USB-A (old, wide plug) to USB-C cable you use to connect your phone to your computer. Try to get one that is at least 1.5 amps though. If you go under that, it might look like the phone is discharging (even though it's not) due to the battery pack not being able to charge the phone fast enough.