Whether the password can be stored on your eReader depends on the device you own.
The eReader-Onleihe was configured to store the login information via cookies. Some devices, such as the Tolino, delete these cookies every time the browser is closed. In this case, login information can not be saved.
Download several ebooks with a Tolino
If you want to download more than one eBook onto your Tolino back to back, there is a trick with which you won't have to relog after every download. Read more here: Download several ebooks with a Tolino