50g battery warning

[HP67]

This is the first set of batteries for this 50g. I'm using Duracells instead of the junk that came in the package. The battery warning has come on but it hasn't died and after sitting off for a while it can do a bunch of work before the indicator comes on again. Does anybody have a feel for how long the batteries have to live when the indicator comes on? I don't want to waste the batteries by throwing them out before their time, but dying in the middle of editing a big program is not very attractive either. I do take backups but history shows the backup you need is usually not the one you have.