IPhone 4S dying extremely quickly?

I updated to iOS 8 a few days after the update released. A few days after that, my phone's battery has been draining at an alarming rate: as I wrote this question, the percentage went from 25 to 19. That's within roughly a minute to a minute and a half.

Furthermore, my phone's battery might go from 55% all the way down to below 20% in a cold room or on a hot day, so temperatures for some reason affect it, usually by draining battery like I said, or through several annoying system failures.

Any reason for the battery becoming so horrible all of a sudden? Is it the operating system? Or something else?
Lastly: no, I do not use battery-draining apps or cellular data much at all.

IOS 8 was made for the iPhone 6. The iPhone 4 can't handle and was not built for that powerful high tech software. It's trying hard to run the program which is causing it to work harder, which means using more energy and power. Hence your battery lowering at an alarming rate!