Just scanned through the specs for U3. I see the value in it. You could buy this already on a board with pretty much everything you need on Amazon:
https://www.amazon.com/Comimark-MCP73871-Lithium-Polymer-Charger/dp/B07V4PHKNX/ref=sr_1_1?keywords=mcp73871&qid=1674263067&sr=8-1