Most batter contains milk and eggs, which can spoil quickly if not used. Batter will also lose its leavening if its left too long.
[header] How to use leftover dough or batter [title] Use batter within 24 hours. [step] Refrigerate any extra batter or dough, covered with plastic, for up to a day. [substeps] You won't want to use batter that is older than 24 hours.