Run my own test with a brand new R617FS just now:
Pre-heated the oven to 80°C. Placed the 4 cell Nicad from my Spektrum and the R617FS in a glass bowl and put it in the oven.
When I took the LED went from green to red I took it out immediately and measured the housing temperature: 70°C
It changed from red to green when the housing temperature dropped to 50°C.
This is an easy procedure everyone can do at home - and it does not take long. It is also much less risky than using a heat gun.
Jürgen