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 Kong....ie, 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
Sony XPERIA ZL