If you are a patient guy, have some experience in fine mechanics and it's not your first encounter with a soldering iron, the fix is not that difficult. (But if you've to buy a soldering iron first, you'd maybe be better off to find someone and have her or him do this for you.)
I was in the same situation like you, my K-50 started to fail when I was on a trip and only some weeks before another one.
After watching the video linked above and finding a replacement in an old laptop's CD drive, I gave it a go and it has not failed again since then.
For the other body, I'd recommend using Eneloops, because this seems to postpone the failure.
With the recent improvements in sensors, the K3ii seems to be somewhat outdated already, so I can understand that you're waiting for its successor.
Last edited by sys3175; 08-04-2017 at 10:01 AM.