Is anyone elses Iphone 5 random with battery usage?

About a week ago. I had accumulated 8 hrs and 20 minutes usage and 3 days 5 hrs stand by time before it was about to die. Today I have almost 6 hrs and 3 days stand by and the battery is at 10%, It seems like the battery usage is really random. One day I have an extra 2 hours talk time the next day my phone dies alot quicker. Could this be from not exiting out apps when i'm not using them or is the Iphone 5 just weird like that?

1. Bravo for watching your battery consumption so closely.
2. As the battery goes through more cycles, you will notice the battery life will even out and become longer. Lithium Ion batteries are rated for about 500 cycles, so you will have years of service as long as you follow #3:
3. Good job waiting until the battery is about to die (1 or 2%) before charging. You will notice this extends the life of your battery over time
4. Wi-Fi draws battery, APPS draw battery and especially LTE Data networks draw battery power. Your phone has access to all three. Talk time is exclusively on 3G networks, so what you are experiencing is some mix of Wi-Fi, APPS or LTE drawing battery power at higher rates than your previous phone.
All normal.