Sadly I must concur.
I've always had excellent battery life with my iPhone 5 w/ 16 GB. Through every iOS version up to 8.3.
I've always updated the phone through iTunes, directly connected through USB. And, I only do so when the phone is 100% charged.
I have always been skeptical of those complaining of iOS revisions decreasing battery life.
Up until 8.3, I wad accustomed to having my phone survive more than 24 hours without needing to be charged. I actually never saw my phone drop below 60% remaining battery life. I charged it when and if I slept. 24 and 48 hour days are typical for me.
With 8.3, I'm finding that I'll be at 50% remaining charge after only 3 to 4 hours of mostly idle time.
If I start with a 100% charged phone, I can have it drop to 80% remaining after about 10 minutes of a texting conversation.
By 12 hours of idle time, the phone will be down to 1% remaining.
I have never seen numbers this low on my phone before I upgraded to 8.3.
All the way through 8.2, I would have believed most were crazy to think that the update decreased their battery life.
Yet, here I am with my usage habits unchanged, and a phone that doesn't get me anywhere near the usage I used to get.
Now I have to plan and minimize my use of the phone if I think I might need to use it 5 or 6 hours from now.
In fact, my phone was just pulled from the charger, and lost 10% just entering this response. That's just a few minutes of typing with the screen on.
Unfortunately, I now have to give credit to those I used to question on this topic.
And, yes I do keep Bluetooth turned off, cellular data turned off, and 99.9% of the time it is within a few feet of a wifi router. So it's not struggling for a signal.
And, I always have a strong cellular signal as well.
Background tasks are all extremely minimized and most removed.
So, for me, 8.3 has meant more time charging, and more time planning my usage to get through a day.