Anker PowerCore 5000, Ultra-Compact 5000mAh External Battery Electronics You can cut this stuff

You can cut this stuff pretty easily with wire cutters

but you can cut the default trace and add a solder jumper if you need to switch to 3

The best part about all this is that the Pi 3 keeps the same shape

And what could make the Pi 4 better than the 3

Anker PowerCore 5000, Ultra-Compact 5000mAh External Battery Electronics You can cut this stuffHigh Capacity: Contains 5000 mAh of power. Enough to provide two charges to an iPhone 6s or at least one to a Galaxy S7. Ultra Compact: Remarkably small, tubular design slides easily next to your phone in any pocket or bag. Just 10cm tall and 3cm wide. High Speed Charging: Equipped with exclusive PowerIQ technology, it provides the fastest possible charge to any phone or tablet (up to 2A). Does not support Qualcomm Quick Charge.