Do I need to buy the Stratus portable connection kit with Stratus ES/ESG?

You may continue to use your Stratus portable receiver independently, but purchasing the connection kit will allow you to take the Stratus portable receiver off the glare shield or window and stow it out of the way when using the transponder. The portable receiver will use the aircraft’s mounted antennas for excellent GPS and ADS-B reception, and will be supplied power from the transponder.