Upgrades do come with risk. But in general, you'll see better battery performance in 8... And even more so in 8.1. Google has been checking in a ton of enhancements to Android.
If you do run into problems, a factory reset will usually clear them up, and the benefits far out weight the risk.
Keep in mind that people often land here when they have a problem... So there is a selection bias... Makes small problems seem like big problems. If only 10 people in the world have a particular issue, but all 10 find themselves here, posting in the same thread they found in a Google search, it might appear that it's widespread when in reality it's 10 out of thousands, or millions...