All updates have a negative impact on the battery life of the terminal and iOS 8 has not stopped. We have a slightly broader view of this problem and understand that the use of the battery is also determined by the pattern of use we make of it, which is why I do not think Apple makes no improvement in this regard in future updates system.
There are many things that we can recommend, but it's best to look at the recommendations we have made in a previous publication and choose the one that best fits your needs and use.