Solution to iphone overheating and excessive battery drain problem
Guys, I had the same problem. My iphone worked fine about 1 month then suddenly started to overheat a lot and battery drains very fast. It was so hot, specially when WIFI was on, that I have to put it on stand-by after just 3-4 minutes to let it cool down.
I also noticed this happened after I installed/removed some game. The iphone overheats a lot when on 4G/LTE and/or WIFI. Did a few tests (jailbroken, hehe), installed a logger and found out the cause.
Location service on 3G/WIFI used hardly by icloud and system services like iAds. Also the so called "product Improvement" which is an Adware installed by Apple for diagnostic purpose but in fact keeps records about what you do. Even when location service is OFF, these trackers work in background using NAND to write the logs, as soon as you connect to WIFI or 3G is on, those logs are uploaded.
Now, what to do.
1. Go to Settings>Privacy>Location Services, turn it on to see all details, then Open System Services and disable Locatino Service for:
-Location-Based Alerts
-Location-Based iAds
-WIFI networking (this drains a lot and is useless)
Product Improvement (Hm, ain't Apple guinea pigs)
-Diagnostics & Usage
-Popular near me
-Routing and Traffic
-Improve Maps
As soon as you disable the above list, turn off the Location Service and keep it off unless you use the Maps or Navigation Apps, etc.
I also disabled the icloud completely as I find it useless for me but you can use it with maximum privacy settings (no automatically merging documents.or images, chose exactly what you allow icloud upload from your phone).
Finally, reboot your iphone (turn off and on). And all will work flawleslly
My iphone 6 runs 8.1.1 btw.. No problemo anymore.