Oh, ok great!
Well that makes a lot more sense thank you for explaining that to me. I had been trying to research that answer for the past 3 months that i have had the phone.
Now when it is asleep(previously connected to wifi) and the phone is roaming with low data in the area, is the phone trying to find data connection? Why I ask is because when I have tested turning off my data during the day and just being on wifi, I will still get all my notifications and I don't lose like 50% battery throughout the day with it just sitting there.
Ok, hopefully I won't bore you with the long explanation for your situation
Lets start with the cellular side only without worrying about data at all. Modern cell phones communicate with the tower periodically for a few reasons.
1) Is a tower there?
2) How much power is needed to communicate with that tower.
3) To see if a tower switch is needed.
4) Report which tower quadrant you are near for incoming calls, SMS and MMS.
You can be 100 feet or 5 miles from the tower and it always does that check list. Now there are a few variables that affect how good of a signal you have. Distance, line of sight obstructions, bouncing/reflective signals, EMI (Electromagnetic Interference) and the number of people already connected to the tower.
So lets use a layman's example to explain how this all works.
I am standing 10 feet from you. You (the cell phone) can say something and I (the tower) should be able to acknowledge you with no issues. Now because you are 10 feet from me, you can use a very soft voice (lower power at about 1/8 to 1/4 of a watt) and I will be able to hear. Now on the other hand because I am the tower you will get a VERY LOUD response back. Why? Because I say (transmit) my answer at my max power because I don't know what distance you are from me.
Life is good. You can last all day (battery usage) at this distance. But as you get further away, you have to talk louder and louder (higher power at around 1/4 to 3/4 watt) as the distance expands. Eventually you will hit the limit of your voice (1 watt of power) and I will no longer hear you even though you can hear me (I have LOTS of power since I am tied to the power grid). As you can see you can end up using up your battery 4 times faster.
Now that is for only you talking with me. Imagine if there are 100 people that are 100 to 5000 feet from me all talking to me at once. Now you have to talk louder (use more power) to get my attention. Now imagine 1000 people near me. You can see where this is going. As the number of cell phones increases more and more power is required to get the cell towers attention. Now to help that, the cell phone only "talks" or "pings" the tower when needed to make sure everything is ok. That helps reduce the power needed to maintain the check list.
But the second you switch to data or voice mode, then the connection has to be maintained 100% and that is where you can get very serious battery drain. So when you switch off cellular data and use only WiFi, you remove that battery drain scenario since WiFi requires much less power than the cellular connections.
Hope that clears everything up.