Hi Greg!
Thanks for reaching Microsoft Community. We're here to help and let's work on this together.
Regarding your query, Smart Charging is an automatic feature, and it will automatically come back on when it detects your device is plugged in for prolonged periods or used at elevated temperatures. For more details on Smart Charging, please see through this link Smart charging on Surface - Microsoft Support.
Thanks again for choosing Microsoft. Hope this helps!
Regards,
RodelioP.