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Thank you for contacting the Intel community.
In this case, any suggestion we can provide it may or may not be accurate since this is an OEM (Original Equipment Manufacturer) system and as you may know the processor is not able to increase or decrease the voltage or Mhz by itself or because the manufacturer decided to be make it like that. The watts and MHz are handle by your system BIOS or system configuration and how Dell designed your system, therefore, they are more familiar how the components in your computer interact with each other.
At this point, the only suggestion I can provide is to do a BIOS update if Dell has a new version for your system but Dell should be able to assist you better.
1) Remove battery
2) Disconnect CMOS battery
3) Reconnect both batteries after a minute or so
4) Reconfigure BIOS
Minimum CPU power is back down to 0.6 watts, & estimated runtime while idling is back up to 12-13 hours.