KPW1 battery replacement

I'm still using my KPW1 released in 2012. Wondering when should I replace the battery (I'll get a third-party to do it in my country). I suddenly don't want it to die on me. I use it couple of hours every day and charge it once every 10 days or so.

If the battery is glued and cannot be replaced, I might get a voyage instead or voyage 2 if it ever comes out.