Varia RTL 515 turn intself off after few seconds . Defected device or battery ?

Have you looked up in the official troubleshooter?
Have you reseted the device?
If options above don't help- claim warranty

Thanks a lot for your advice. I have checked troubleshooter, forums, I have reseted device many times. After reset device works a bit longer ( 20 seconds ?), later only aprox. 3 seconds. 
I am going to claim warranty …..

Unfortunately, looks like hardware issue. From my experience, garmin will replace your device with no hasitation, you just need the original receipt (and you'll probably have to pay the shipping)

the same thing happens with my rtl515 when i try to pair with edge 1030. did you manage to solve it?

I have same issue here, looking for a solution.

I had this happen to me on a 510 and it turned out to be a bit of dirt / dusk stuck under the button. To fix this I pressed the button a couple of times (without turning the unit on) and the carefully held it under running warm water. Let it dry completely and see whether it fixes things.