Question Where to get a new battery for Xperia ZL

Hey guys,

Where is the best place to get a brand new battery for my Sony Xperia ZL. I want genuineuSonyny battery, not a cheapo battery from Hong, eBay. My phone is having random shut offs and it's getting frustrating. I downloaded an app that checked the battery and I can see the battery is the issue. I'm going to call Sony to see if my phone is still undewarrantyty or not. Any info would be great. Thanks