In most cases, a more powerful inexpensive phone would cost less than trying to replace the battery. Heck, if you value your time a new phone is probably less expensive that trying to salvage an old one.

They also told me on reddit, that it is probably not such a good idea to buy a cheap battery for a device, that has a battery that is not meant to be removed, because the resulting cheap quality may make your phone go up in flames.

Anyway, there are still so many devices where you can remove the battery out there.

And not everyone has money as highest priority, so I'd rather take my time and buy a new battery for an old phone than throwing it away and creating unnecessary electronic waste, just to save a few bucks.

Plus when you buy a new device, you will need some time to transfer your data, and set it up again, possibly experience new bugs and what not. So that also costs some time.