Can we use AA 1.5v 1000mah battary at the place of C 1.5v 1000mah battery in laptop

Although it is quite possible for the batteries to be interchanged, you will find that a AA battery will be consumed quite a bit faster than the C battery. If you were to put several AA batteries in parallel, then they would last longer. This is true for any battery. The largest obstacle I foresee is reliably connecting AA batteries where a C battery belongs.

Good Luck.