Well, after some short tests and now a little longer test last night i can put out some resume:

+ The Flashlight is bright and illuminates pretty good for example when doing something at night on the balcony etc.
+/- the Battery holds up around 1 hour i would say. 240mAH 9V Rechargable.
- The LEDs get hot, i knew that, but didn't expect them to melt the hotglue again, even with open lid

So for the next iteration i will:

- Use bright white LEDs not the warm white ones
- i will somehow bolt the LEDs that the don't get loose because of the heat
- Constant Current instead of constant Voltage.
- And for that i might have to use 2x9V Blocks.....
- i would like to add a charging mechanism, so that i can recharge the battery while it is plugged in.
- Maybe i add a fan.... but that i would like to stay fanless....

Maybe i need a bigger enclosure....