Why iPhone 5 battery is dyeing super fast?

I woke up this morning after charging my phone overnight, so it was 100% at 5:30 am. I've sent 2 texts to my husband and 2 to my mother. Bluetooth is off, I'm connected to my Wi-Fi so i'm not searching, yet it's now noon and my battery is at 62%. Any ideas what is causing the battery to drain so fast? I've never had Siri so I don't know if that causes it. I thought about roaming and updating towers but I try to dial that and a pop up says I'm unable to dial that from this phone? I'm wondering if anyone else has come across this problem and been able to fix it. I made sure my phone was fully charges also before I activated it.

Some batteries have a shorter life span then others looks like you need to replace it sorry

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