Batch management (urgent)

Dear All,

I maintain batch level as a material, now i am creating five purchase order

for ex p1,p2,p3,p4,p5 and respective GR1,GR2,GR3,GR4,GR5.

But i want the same batch number (single) for all GR.

what customization i have to do?

Please give the feed back early

regards

raja