This is a whole lot of questionable forum resource allocation and effort. You can get just about any capacity and form factor battery today, just as the manufacturer of your widget did. You don't need to know much at all about it, just the type and measure it with a caliper so the replacement fits then swap over the protection circuit if part of the batt pack instead of integral to the widget.
It's not at all worth being a slave to this when you could either find some way to apply mountains of silica gel [
] or just buy a new battery when the time comes. A battery this size is going to be single-digit dollars expense. If you can't solder that, the topic is out of place here but it was already when the basics of Li-Ion lifespan are easily found with a web search... except for the magic of silica gel at critical mass, you won't find that anywhere but here.
This is just another silly waste of time where the OP wants some magical way to make everything last forever. YOU will not last forever, your time is finite and worth too much to indulge in this OCD.