That is the electrical connections for the battery grip. You pull off the rubber grommet, put it on the grip storage area and mount the grip by screwing it into tripod mount hole.
Interesting! I'm used to a long part that goes into the battery compartment! Thank you!
About the Pentax grip:
The "standard" battery stays where it is.
The grip takes the second battery. You can swap the 2nd battery without turning the camera off, provided that the camera battery is in place and charged.
The grip's battery tray comes with storage space for a 2nd SD card (just storage not a reader). It's a feature that has saved the day a few times for me.
It also has a second tray for AA batteries, should you be travelling far away from a power outlet.
Handling is a personal thing, but after i put a grip on my K5, i never took it off again. It's better balanced and much more natural when shooting vertical. Plus you get double power and a spare SD...
