Do I need to attach lid battens if...

[Brian Penning]

...the top of a newly made blanket chest is perfectly flat now?

Note: It's for a client so I don't want to have to attach them later.

[Chip Lindley]

An Ounce of Prevention is worth a Pound of Cure. Attach the battens now. You will be glad you did; wood movement being what it is! And make the outer screw holes elongated to embrace any of the movement just mentioned.