FYI, there's a relatively new ~10000 mAh version of that battery that's the same physical size should you need it.
As for I2C. You mean pins 3 & 5, right?
https://www.raspberrypi-spy.co.uk/2012/06/simple-guide-to-the-rpi-gpio-header-and-pins/Everything just gets connected together: 5v pins on the Pi and each I2C device connects together, ground pins connect together, SDA pins connect together, and SCL pins connect together.
Each device will have a specific address. It's part of the hardware. There are some devices that let you program their address, but they aren't common. Some devices support a small range (2, 3, 8, etc) of addresses. Those you can wire to set which of the supported addresses it will use.
That battery gauge is only at address 0x0B. The piRTC appears to only be at 0x68. So neither supports having their address adjusted. But that's fine in this case since they use difference addresses.
You would need to use them as I2C devices. The windows IoT core should have support for working with I2C devices. For reference you can look at the Adafruit drivers/libraries for those devices. it's all on GitHub. It doesn't matter what the host hardware or OS is; the I2C interaction will be the same.
Dave