Both .nba and .nbi files are backups produced by Nero BackItUp software. Whilst probably not possible to convert one to another, you could perhaps recover the contents somehow and produce a new backup. Anyways, only the original software will be of help here and no 3rd party products can help you.
Convert Nero BackItUp archive to Nero BackItUp backup information.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert nba to nbi on Windows
Nero BackItUp is backup utility that was a part of Nero Suite. However now is distributed as standalone backup application for Microsoft Windows. NeroBackItUp is able to backup selected important files and operating system, as well as all hard drive. You can stored backup data on any other hard disk, burn them on CD, DVD, Blu-ray, HD DVD media, or saved on USB flash drives.
Convert from nba file
to nbi file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.