Lumia 1520 battery saver test terminated after 4 days, 9 hours, with 20% charge remaining. So it's not unreasonable to expect five to six days from a full charge when battery saver is on. for at least three hours yesterday the device was used a a camera, viewing & editing photos, as well as uploading them to OneDrive when a wifi network became available.
I had to connect the thing via a USB cable to get the pics off it, I could have downloaded them from OneDrive but that's a waste of bandwidth/time.