> Most people I know only get new phones because their battery will no longer get them through the day

I don't disagree with this, but I also think it's because the battery often dies around the time most people would consider upgrading anyway. The battery isn't the only reason people upgrade, it's just a forcing factor.

If batteries normally last 3-5 years, I don't think we're going to start seeing most people keep their phones for 7-10 years. I still think we're going to see people upgrading around the 3-5 year mark. I would point to the current market as evidence of this. An iPhone battery replacement is somewhere between $50-$100 right now which is drastically cheaper than a new iPhone and yet we still see the 3-5 year upgrade cycle. Maybe making it something you can do at home in a few minutes will result in a few more people just choosing to replace the battery vs the entire phone, but I don't see it drastically changing things since a cheap alternative to replacing the phone already exists and yet we still see the 3-5 year replacement cycle.

> If batteries normally last 3-5 years, I don't think we're going to start seeing most people keep their phones for 7-10 years.

I think they will eventually. People hang on to their computers for longer and longer because old ones are just good enough. Phones are getting to that same stage in their evolution where they stopped evolving by leaps and bounds between generations. A seven year old phone like an iPhone 11 for example is perfectly adequate for a lot of people.

There are two real blockers from keeping a phone for so long, official software support and battery life. If some big manufacturers solved the first with extended support cycles, which is an expensive one, why not solve the second too?

> I don't think we're going to start seeing most people keep their phones for 7-10 years.

I do. I lasted more than 15 years on 2 phones, and the only reason I'm at my fourth right now, is because the third was stolen after 3 months of use. I'm hoping its replacement, a used phone already, will last at least 5 years. Regardless, my next upgrade will not be a choice. I will milk my current phone until I am forced to change, as I always do.

We're going to start seeing people keep the phones longer and longer. It used to be people were amazed at the upgrade between iPhone versions, and now they struggle to identify a difference.

Other than a few people who absolutely must have the latest phone, I only see two reason why people replace their phone: 1) Battery is no good. 2) Operating system has stopped getting updates and they can no longer run that one or two apps they really need.

Replaceable battery and 10 years of OS updates and a large percentage of people would stop upgrading their phones. There hasn't been much innovation in phones in the past 10 years. If the battery hadn't died and the OS was still updated there would be zero reason for me to not be using my iPhone 7.

> most people would consider upgrading anyway

most people would buy one phone and keep it forever if they could, because most people can't actually afford to be replacing their phone frequently.

The only reason they do is because they get slower, or battery gets worn out or whatever else. If their one phone actually lasted forever they would likely happily keep it forever

Sure, batteries dying are just one way in which phones become disposable. But I want to fight all those ways too (stupid new protocols and lack of security updates notably).