Never heard of the tool, but by the sound of it, it extends your battery life by letting you not charge to 100% (e.g. only charge to 80%).

That’s real. Doing that will prolong the life of your battery.

Should you pay $25 for a tool that will do that? Well, if you’re on Android 12 (edit: and your device manufacturer has implemented it), there may be an option in the battery settings to limit charging to 85% which gives you most of the benefit.

If you’re not on Android 12 but have a rooted phone, you can get a free app that does the same thing.

If protecting the battery is important to you, you don’t have a rooted phone (and don’t want to root it), and don’t have Android 12, then as far as I can tell from reviews, Chargie does do what it says.