A future Apple Watch could allow the watch body to detach from the band for charging while the band continues to track Biometrics+
Today the US Patent & Trademark Office published a patent application from Apple that relates to an Apple Watch Band that will be able to function as a biometric device tracking a user's heart rate, a respiration rate, blood oxygenation level, a blood volume estimate, blood pressure, even when the Apple Watch body is detached for charging or other reasons....
Source: patentlyapple.com