Is it safe to upgrade to iOS 7?

I used to have an iPhone 5 which I updated to iOS 7 & then iOS 7.1.1 which I did straight away as soon as I got the phone. The phone turned out to be second hand used and was replaced by Apple Store under UK consumer law, there was a fault with the phone that I found out it was used, when the home button stopped working, but at the same time I had severe battery drain issues, where the battery would be completely drained in 20 minutes and even the aid of a Mophie battery case the battery was dead in 3 hours so I even got a DNS power pack too.

I now have a new iPhone 5 on iOS 6, the battery performance is not great either, to test it, I used the screen at full brightness & never turn off, location services turned on and currently have 4 hours. 46 minutes of usage with 7 hours of standby.

So I do not want to ruin another iPhone, is iOS 7.1.1 safe to upgrade to? Or is it best to wait for iOS 8? And do current iOS 8 users on beta program have any issues with battery performance yet?

I really liked iOS 7 and iOS 8 looks really good from the demonstrations I have seen, but really do not want a poorly performing battery

IOS7 should be fine, one of the initial updates to that fixed the supposed battery drain problem.

The battery will go flat in a few hours with the screen active, no matter what operating system.

Mines getting on for two years old, with ios7 & all updates. [Edit - iphone 5, 64GB].

I have Wi-Fi, Bluetooth & location etc. Permanently enabled plus a Pebble smartwatch linked to it & the app for that permanently running

The battery lasts about two days with just minimal phone call use. (It's about three days without the pebble app).

The only times I have battery problems are when I forget to close other background apps - especially something like a navigator program.