Arduino Fio: Battery/Solar Powered Weather Station I am trying to make a Solar Powered Weather Station. I'm using the Arduino Fio, with a BMP180 and a DHT22 as the sensors. There are sleep modes activated with the Fio and the Xbee. It seems like the battery capacity requirements, after measuring, around about 664 mAh per day.

The Fio has a built in LiPo charger (MCP73831/2). Is this 3.7V 2000mAh battery safe to plug into the Fio as its battery source? Here is the datasheet from the link just provided. I'm not an engineer and I want to make sure that this is a safe device.

Once determining the correct battery, I will like to pair it with a solar panel.

Thanks for the help
You have a LiPo charger module. It's meant to charge single LiPo cells. It is therefore, the intended safe use that you can connect any single LiPo cell to it. All single cell LiPo batteries are nominally 3.7V. The only real question might be -- does the charging circuit try to charge too fast?

A 2000mAh pouch LiPo can safely be charged at 1X the capacity. So a maximum current of 2000mA for an hour in this case. The battery management chip has a maximum charge current of 500mA, so there's no way it can reach over 2000mAh of current while charging.

The datasheet for the battery management chip shows a R_PROG resistor that basically sets the maximum charge current.  Section 5.1.2 shows the formula for charge current regulation at:

I_REG [mA] = 1000 [V] / R_PROG [kΩ]

The schematic for the Fio shows they have used a 2k ohm resistor.

Thus: I_REG [mA] = 1000 [V] / 2 [kΩ] = 500 [mA] (the maximum the chip can operate)