Hi there,
Nah’ 
Looks like a WIP to me 
You do what you can do, with what you got, No Shame in that game! (post limit will lift and you can post pics after a few posts, btw) I see the Dropbox files. 
SO what I see is your NOT using the battery connections on the bottom of the Xiao? Why NOT?
All bets are off if you choose to not power it that way, the other methods require a diode and
other considerations and will NOT get the LOW numbers NO-WAY!
Yada, yada , Boooster , Buck converter it’s all been done before not a big deal.
(honestly I LOL because all the first attempts are like yours , me included and look this way…WRONG…LOL!) 
the smaller CR2032 coin cells will get you 350-450 ma. run time current total then it’s down hill and done from there. I like the 2450 has more juice longer and supports more total power draw.
During the advertising phase of the BLE the Xiao uses the most current. so the Idea is do the (setup) heavy lifting for the connection right away and then go Sleep. “rinse and repeat”
mind you many optimisations can be made to the BLE connection parameters and settings to squeeze the max out of battery life.
In your code if you are using the Serial port or “while Serial” the port will wait until a USB cable is connected and the rs232 driver/rec 1488/89 are in MARK state and using 1.x ma. of current.
Have a look at the schematic for the Xiao and READ the Links to @msfujino 
research on “System on SLeep”
BSP… Board Support Package there are two Mbed versions (2.9.1) & NON-mbed versions(1.1.1) to start with.
have you gone over this: ?
Are you SURE you read the Wiki?
Two Arduino Libraries
Seeed Studio XIAO nRF52840 assembles many functions in one tiny board and sometimes may not perform the best of them. Hence, Seeed has published two Arduino libraries to let it maximum the power of each function. Therefore:
- It is recommanded to use the
Seeed nRF52 Boardslibrary if you want to apply Bluetooth function and “Low Energy Cost Function”. - It is recommanded to use the
Seeed nRF52 mbed-enabled Boardslibrary if you want to use it in embedded Machine Learning Applications or apply “IMU & PDM advanced function”. - Both libraries support very well when it comes to the basic usage, such as LED, Digital, Analog, Serial, I2C, SPI.
The Pin definition supported by these two libraries might be a little different and Seeed will keep update the wiki until it is clear.
Stop and take the time to RTFM 
is the best advice your close but your missing the basic understandings it will clear it up or generate the right questions to help you.
then you can get these:
LINK
HTH
GL 
PJ 