Mick or anyone else that understands batteries...Riddle me this: I have a 2014 Droid Turbo w/ 3900 mAh battery. I'd say first 1.5 years the battery was good. Since then it's been losing steam and the need to charge up is a lot more frequent. Fast forward today you have most flagships that float around 2,700-3,300 mAh. Is it possible that despite the smaller battery on these flagships, they are better optimized, more efficient chipset, better LED/lighting, which would then net the same effect of a phone with 3900 mAh? Or am i way off base?
Most important consideration for battery size is the screen surface area to battery mAh ratio. This should be understandable because the screen remains the #1 battery drain for virtually every user (regardless of device or operating system) in existence.
Next most important hardware spec is your chipset. More powerful chipsets are bigger drains, so the best phones tend to require larger batteries just to enjoy the same battery lives.
Other than that, battery conditioning has changed the least among all technology types since the inception of the whole iPhone revolution. Everyone is waiting for this dam to break open (tons of money and other resources being poured into R&D on stuff like the glass battery designs). But otherwise, pretty much everything runs on the Lithium Polymer technology, and the battery will simply wear down over time due to all the recharges.
The industry has focused more on making the LED/LCD cells more energy efficient, not the other way around. OLED displays have always drained more energy per cell, so this has been an area of particular concern for the Android manufacturers like Samsung and LG (although Apple has finally transitioned to an OLED display with the
iPhone X).
Beyond that, Android phones tend to build up a ton of advertising spam. So every time you open an app, all of those pop-ups, and also hidden processes, will drain the battery. For this reason Android phones out of the box will often enjoy much, much better battery lives than ones that have built up a user profile. Apple's ecosystem (most specifically its revenue structure) works in a way that they are much better able to control and stifle this sort of software spamming. Expert users with root access often block these ads and hidden processes from running, but that's a niche market.