I used years as an example- in reality it was maybe a month or so and I lost my save game. It was due to being frustration of the end boss in Book II. I don't have foresight in to other games I'd play, but the point is something with a real battery save that actually has a chance to last.
Anyhow, if I were to get one I'd likely just replace the battery right away. To be clear, it WILL work on the US Turbo Duo? Are there any alternatives to it? google seems to indicate there's a version 2 of it, and maybe some other things. I was under the impression that the pinout on the HU card slot on the Duo was reversed from Japan which is my concern about it not working.