scrap battery treatment in accounts and gst??

Dear Experts !!

I need help with accounting entries in GST in general. I buy battery, for example, "A1" for Rs 5000 + 28%

Then I sell this battery "A1" for Rs 5800 + 28% .

I give a discount of Rs 1500 to Customer on returning me old battery. Effectively I get Rs 5924 in hand and I have a scrap item valued at Rs 1500 in stock, which I often used to sell for cash and ignore accounting for that.

These entries were fine until now, but in GST I want to make it truly accoutable.