Susan, different batteries perfom differently over their "lifespan".

Alkeline (and I think carbon) do not do well no "high drain" applications. Once they have drained a little, as pdq said, although they might test out OK on a tester and perform OK on something else, they are not really able to produce the higher current for long.

If it is a "higher drain" device and it will work on rechargeable NiMh, you would be much better off using those. They cope better in those conditions.