Lying / iPhone warrantee doesn't mean a thing

I have an iPhone 5S, bought in April 2014 from Vodacom. At not even 10m old the battery drains from 100% to 19% overnight, with no apps, WiFi or usage - just standby. My iPhone 5S's battery went from 100% to 89% in the same period while I continued using mine.<br> <br> I took it to Menlyn and it was sent to the advanced repair centre. A week later I went to pick it up - it was \returned not repaired". Apparently the battery is just fine. Their diagnostic test must have just been to check that the phone has power. I complained and said that I've tested the battery lifetime thoroughly to make sure it was the battery and not actual usage (one can also check this on the phone's stats)"