That's the generation of Particel devices
If you are not locally building from the mesh-develop branch of the open source repo, you probably are testing the "unimplemented" sleep modes which are currently documented as
https://docs.particle.io/reference/device-os/firmware/argon/#sleep-sleep-
So calling System.sleep() will render unpredictable results.
Iām currently running an adafruit solar charger (https://www.adafruit.com/product/390) and buck-boost (https://www.adafruit.com/product/2190) on my photon and its working great. Monitoring the battery level with a simple 2:1 resistor/divider.
I also have a DFRobot Solar Power Manager 5V (https://www.dfrobot.com/wiki/index.php/Solar_Power_Manager_5V_SKU:_DFR0559) on order, and hoping to be able to use that to reduce costs a bit. My panels are 6V, which is at the max upper end of the DFRobot input range, so weāll seeā¦
I also have a project where I am using the Electron and have simply wired VIN to the 6V panel and its working great. If you look closely, the electron accepts a much wider input range (5VDC to 12VDC) as opposed to the photon (3.6 to 5.5VDC) and argon which doesnt even technically have a VIN and only has the USB power pins exposed. I have to say working with the Electron has been very nice in this case, and obviously has a much better/more complete charge circuit then the Gen3 devices. Would have been nice to have the same ability on Gen3 as on the Electron, but of course that adds costs. When I saw all Gen3 devices had lipo ports, I was excited this was already built in though 
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The Gen3 Boron has the same Charging circuit as the Electons.
Then how can I supply up to 12v like the electrons?
Supply it to the Vin Pin.
Just for clarity, 12V is only safe for Vin for the Boron in Gen3, not the Xenon or Argon.
Please correct me if Iām wrong.
Correct. Only the Boron has the same PMIC chip as the Electrons.
I suggest a datasheet update, as its not at all clear this is possible!
In version 0.9.0 sleep is available for Gen3 devices
3rd-generation devices (Argon, Boron, Xenon) only support sleep modes in 0.9.0 and later. Sleep does not function properly in 0.8.0-rc versions of Device OS for mesh devices.
Reference
I'm trying that this weekend.
Is this not summarized anywhere in reference material? It seems (especially with gen3 stuff where there's a micro-usb header) that the ability to pipe in other voltages safely should be well detailed so there isn't confusion between the boron and the argon/xenon models.
The input voltage range for the Boronās Vusb pin is not clearly documented. However, there is a schematic and bill of materials to reference. You have to look at the PMIC datasheet to get the max voltage range for that pin. I suggested an update to the docs on this specific point before:
