Valve announced the Steam Frame alongside the Steam Machine last year, and though we still don't have firm release dates or final pricing information (likely delayed because of global memory shortages), Valve has been jumping through hoops on its way to release day. That includes FCC certification, which gives us official filings to pore over. These have revealed some intriguing information about the headset and its accessories.
Mentions of the Enthusiast Kit appear in the health and safety manual. It reads that the "controller triggers, face gasket attachment, and the Enthusiast accessory battery pack include magnets." It goes on, "The Frame Enthusiast kit also includes a hot-swappable lithium-ion battery pack," and warns users to "use only the battery pack that came with your Enthusiast kit, or an authorized replacement battery pack."
The standard Frame has its own battery, but it sounds like the Enthusiast Kit upgrade pack will include at least one additional battery that can be hot-swapped during use. It's not clear whether an additional internal battery will prevent hardware shutdown when the standard battery is removed, or whether the Enthusiast Kit will replace the standard battery with a swappable one.