The HP ElitePad Expansion Jacket is an accessory designed for the HP ElitePad tablet that adds additional functionality and connectivity options. The HSTNN-C75J is the part number for the HP ElitePad Expansion Jacket without battery.

The Expansion Jacket provides additional ports and features, including:

Two USB ports
One HDMI port
One Ethernet port
One SD card slot
One headphone/microphone jack
One integrated battery for extended run time (not included in the HSTNN-C75J model)

The HP ElitePad Expansion Jacket without battery (HSTNN-C75J) is designed to work specifically with the HP ElitePad tablet, and it connects to the tablet via its docking connector. It does not include a battery, so the integrated battery in the tablet provides the power for the jacket's additional ports and features. The HSTNN-C75J model is ideal for users who already have a separate battery for the HP ElitePad tablet and do not need an additional battery in the Expansion Jacket.