All credit goes to EskildJ
To remove the battery
Get a 15mm nut. Drill a bit into the threading using a 10mm drill. This Tool will open the battery compartment:
So you can see the nice 6*18650 pack, and if you hoped that the charging connector was Water-tight, it isn't.
To get to the switching ring, you don't need to dismount the battery.
To remove the front
You can't simply unscrew the lamp at the battery indicator. You need to remove the reflector first.
Remove the glass holder ring:
You need to make a Tool to unscrew this. I did like this, and it worked fine:
After removing the glass, you see the glass o-ring. You are now at the reflector. unscrew it to get it out.
You can now un-screw the front part of the lamp, threading is in front of the battery indicator.
Notice the two green O-rings. Remove the two green O-rings, and you can slide forward the battery indicator ring:
Then remove the switch ring, beware of the spring/ball:
Notice that the LED window is only single or-ring secured - I guess it is OK, as the Water will compress the plastic opposed to the alu. But it needs to be clean!
Now, the magnet is visible. It is a round disc, 5mm diameter and around 1mm thick.
It is very visible why it is weak. It is corroded away. This could also explain why some people complain about sand under the ring. The "sand" could be disintegrated magnet.
