Thanks for the link!
But even if the battery is dead or I would loose the cal data while changing it, I could do a full calibration. I have access to a Datron 4808 DMM calibrator at the university. It has almost all options. Only the extended current option is missing. So it`s possible for me to calibrate the HP3457A, as I did with my HP3468A and HP3478A.
I also already have a 3V lithium battery I bought from ebay priviosly for my HP3478A, where it wasn't needed. So I don't have to wait for a replacement if neccessary.