Actually inserting a SIM card does a lot of things, the power spike caused by PA is not the only drain on the system.
And remember that the device can also register to the network without a SIM card at all; as 112 calls need to be made at any time regardless of the device lockstate or SIM state (or presence)

So, I assume this could be the scenario leading up to problems when simcard is inserted;
- the device notices a SIM insertion notice
- baseband processor (or integrated baseband process) starts running and allocating air resources

So I just got n9 from my friend. Used and old.

My phone on his battery still turns off when the sim is inserted.

His phone with my battery works perfectly fine.

So we can rule out the battery. Any ideas?

Problem with baseband.

But hang on, did you not say in post #44 that you bought another N9 and that that unit behaved the same way? Did you try your SIM card in your friend's phone? And the other way around? Are both SIM cards from the same provider?

No, I just bought one unit that have this "defect". I've already tried different soft's, batteries, sim cards and still no luck.

Some people here knows that I'm just simple person filling this community. I have some basic understanding about software and hardware and how those things cooperate. But I'm no expert. Maybe I can bring up some game if it comes to the n900 and lower tablet models

N9? Sorry, I would really like to know more but I don't. Maybe I can figure it out for myself but I already did what I could and know how to do.

As you can see, no effect. Maybe some could point me into right direction? Some advice? What to test, what to check inside? (Yes, I can handle a screwdriver).

As in polish tradidion I could buy everyone who could help me a bottle of vodka if I knew any of you personally

I've had 2 N9 with broken CMT (ie - modem). One would simply reboot after entering SIM PIN - you can try adding PIN to your SIM and see if it will reboot when the SIM inserted or after the SIM card is unlocked. Second N9 lost connection to CMT altogether - you can confirm by trying to flashing your device - flashing CMT will fail if that's the case.
In any case I haven't been able to fix any of my devices

Please read Carefully cause everything I wrote is need to understand. I'm polish native. Recently bought chinesse new n9, that after 2 days of usage turned off and refused to cooperate.

Yesterday I came back (from Poland) to Niederlands where I work. Took with me the n9 with polish sim card. Turned it on and it is working for several hours now. Everything is fine. I also tired to turn it on before journey - no luck.

Can someone elaborate?

Not possible to say much without any logs.
I'm still betting on baseband problems though.

Maybe there is something wrong with the modem. I got one random turn off already, but to be honest I still have no real data to troubleshoot the problem.

Maybe the problem is associated with range, here I got full bars in my hometown? Let's say it is a problem to get good range. But if so, problem may lie in power system not the battery itself.

I will try to gather some info as I go, but for the time being I dont even know where to look.