at what voltage to you discard primaries?

Putting a fully charged Alkie in a low drain device is risking leaks a lot more than putting a half charged one in as its total lifetime is shorter, say 1 month in high drain and 6 month in a low drain against 12 month in a low drain only.
The only leaks I have had is in things I tend to forget about, kids toys that are no longer played with etc.

Cheers David