Sadly, it’s not just the batteries, there’s plenty of software stuff too.

Many phone manufacturers will release updates for only 2 years, if you got the most expensive flagship model; otherwise it’s just 1 year. So if you like having the new features of the latest version of Android, you need to upgrade hardware every year.

What if you don’t care about cutting edge software? Fortunately for you, a 3 year old phone should still receive security updates. For example, Samsung knows that many people don’t update every year. If you don’t support them at all, it’s going to be like Windows 95 all over again, and that would be bad for business.

Eventually, even the security updates will stop, because testing new software for a model that is used by only 0.1% of your customers takes a disproportionate amount of time, effort and money, so phone manufacturers simply can’t see the profit in that. If you get one of the enterprise models, you can expect to get firmware and security updates for 5 years. If you got a consumer model, expect much less than that.

Apple is a bit different, but I don’t want to make this wall of text any longer than it already is.