There are some scenarios I can think of that will put strain on an older battery:
- gaming
- recoding a movie
- Foreground and background tasks, such as listening to music or youtube while surfing.
- doing any of the above in hostile climates: such as Phoenix Az.
As long as usage is efficient, reading some material from your device without using any signal, low brightness...yeah the battery should support you.
My point is that this usage you describe will strain any battery, even one on the most efficient iOS version, the original one, even with 100% battery health.
Like I’ve often stated, people have used 1st-gen iPad Pros on iOS 9 for full-brightness Procreate and they get 4 hours (again, on iOS 9).
This is well-known, and independent from battery health or iOS updates (which, if the iOS version is adverse, will make the device unusable. Use an updated 1st-gen iPad Pro for that and you’ll be lucky to get 2 hours, if that), but it doesn’t mean that battery life on iOS 9 is amazing with that usage: it’s not.