Done My Research Just Need Some Guidance on Batteries

Current kid that Im about to start with is

• Meteor 75 Pro Analog (No O4)

• Radiomaster Boxer

• 4 18650 Unprotected, 3200 mAh, Button Top batteries

• Will get on a simulator soon

• Skyzone Cobra X V4 5.8GHz FPV Goggles w/ SteadyView Receiver

Regarding the 18650 batteries, the RadioMaster takes 2 at at time. I noticed in the Start Guide, it wants me to fully charge a pack of batteries, then ensure the antenna is fully connected before powering up for the first time. My question is can I get these batteries, stick them in the Boxer, then connect the Boxer with the USB-C cable to charge the batteries before powering on for the first time? Or should I get an external battery charger for this? Is this what a WhoopStor is for?