Batteries can be replaced for much cheaper than a new phone. Also what good is the warranty if the phone is working. Typically if a device gets past the warranty period, it's probably going to last years unless you do something to break it. I'd rather keep my device longer and just buy a new one if/when that one fails. If you keep the phone for years, the trade in starts to matter less anyhow. Not sure the actual number, but if it's 50% like you suggest, then that's buying a new phone outright every 2 years without trade-in. I'm at the point now where I'm keeping my phone 5 years, and might be 6 now for my 12 Pro as I'm leaning towards still keeping it another year. That's still cheaper in the long run if you just take care of your device and use it as long as you are able. It's also less wasteful of resources, so better for the environment.