I am ready to close AP for the year-end, but I have a couple of open invoice batches with transactions for the new fiscal year. The system is telling me I must post them.

? If I do, where will they be posted? I don't want them in the year I am closing.

If I post them, I assume I should retrieve them into the next year's GL.

You must post them. If you are using GL v9x you can retrieve them into the Next Year (assuming you have this active).