I got myself the iPhone 5 at the start of December which was an ex-demo unit. I've noticed of late the charge in the battery is not holding as well as I'd expect which I assume comes down to its life as a demo phone.
In regards to replacing the battery, I've asked a few places around Hamilton and had quotes ranging from $80 to $120.
Looking at Trademe I can see DIY kits for around $20, even on Amazon.com for $3.34 USD.
I can likely take the phone back to Noel Leeming but would be without it for several days, but given the price of the DIY kits is there much risk using an aftermarket battery or best to stick to genuine apple?