IPHONE 3GS 16gb Spares/repair ?

Hi i have my apple Iphone 3gs 16gb , suddenly stopped working and wont charge , have taken this phone to a engineer who suspects battery failiure ... phone quiet simple to fix and as the screen has no scratches i am going to let go for £40 . im sure to someone who knows what there doing will be a doddle to fix .. thankyou any quiestions please call.