You will find a detailed description and operation of the HPP4 in the manual.

You can choose from a 12 Vdc or a 5 Vdc operating voltage on the relay.
The 5 Vdc variant already works from 4 Vdc to 9 Vdc
The 12 Vdc variant works from 10 Vdc to 24 Vdc

The HPP4 is V-switched which means that the relays use a joint V +.