How long can I leave leftover cake batter in freezer & use again?

I don't know of many people who freeze the batter, though I know Debi did an experiment with it once and it worked fine.

I would not think for more than a few weeks, if that.

I'd assume it would probably be best to bake the cake and freeze the cake, not the batter.

Though that's my best guest as I have never done it.