I found the battery life to be the same.

But the software devs will always more-than use up any extra efficiency, so it'll still barely last a day, and will die early when it gets heavy use...

This varies a lot from app to app. It’s true that some are built in a way that puts no thought towards efficiency, but there are plenty that are built by devs who care.

I like to keep around test devices that somewhat represent the average user’s device, and when it’s practical a low end device and test against those every so often just to make sure the app performs reasonably well.

This has been in my experience more important for Android apps than for iOS apps, though, because the gulf in power between currently-sold devices in the Android world is vastly more large than in the iOS world. With few exceptions, I find that reasonably efficient apps tested and developed chiefly on newer iPhones work fine on older iPhones, but developing and testing an Android app only on flagships will make for a miserable experience for users of low end or older Android devices.

The CPUs (and the software) are so efficient now that only the screen and the radios really consume energy. If you find yourself blaming high CPU usage for low battery life, it's likely you are either incorrect, or the problem is just some bug in the application, nothing intended.

Okay - App devs find yet more reasons to ping their server every 5 mins and keep those radios active...