Hacking Did I brick two 3DSs, or they both have dead battery?

[karikatourea]

I have two 3ds that I haven't turned on and played in quite a while, maybe 4 years. They both have CFW.
On the meantime, since we upgraded to Nintendo switch , I... foraged the sd cards of both of them. I made a backup of the files, formated and plugged the SDs to the switches.
But I got a weird urge to play on the 3ds the other day. I turned it on, and I got greeted with a black screen for a second and then it powered off. Same thing with the other ds too.
To be specific: If I have no sd inserted, it powers off .

If I have an sd inserted, it powers off .

If I have a card adapter on the slot, but no micro SD inside it, the blue light stays on, and so does the black screen of death.

I can't manage to activate god mode or save booting either, but I'm not sure if I know what I am doing, I might have used the wrong keycombo.
I also tried putting back the files on the sd (and I'm freaking out because I can't find the back up for the second 3ds), but that didn't do it either.
And I guess there's still a chance that the battery or some other component is dead after 4 years of just sitting on a self.

I don't know. Any ideas and suggestions are super appreciated.

 

[zfreeman]

It sounds like your 3DS is trying to boot, but it's not following through. You may have accidentally updated firmware, and broken CFW compatibility. Download and replace boot.firm on the root of your SD card.

https://github.com/LumaTeam/Luma3DS/releases

If that doesn't work, follow 3ds.guide, using an ntrboot cartridge when doing so. This will ensure that the CFW bootloader is updated.

https://3ds.hacks.guide/updating-b9s.html

 

[The Real Jdbye]

I have two 3ds that I haven't turned on and played in quite a while, maybe 4 years. They both have CFW.
On the meantime, since we upgraded to Nintendo switch , I... foraged the sd cards of both of them. I made a backup of the files, formated and plugged the SDs to the switches.
But I got a weird urge to play on the 3ds the other day. I turned it on, and I got greeted with a black screen for a second and then it powered off. Same thing with the other ds too.
To be specific: If I have no sd inserted, it powers off .

If I have an sd inserted, it powers off .

If I have a card adapter on the slot, but no micro SD inside it, the blue light stays on, and so does the black screen of death.

I can't manage to activate god mode or save booting either, but I'm not sure if I know what I am doing, I might have used the wrong keycombo.
I also tried putting back the files on the sd (and I'm freaking out because I can't find the back up for the second 3ds), but that didn't do it either.
And I guess there's still a chance that the battery or some other component is dead after 4 years of just sitting on a self.

I don't know. Any ideas and suggestions are super appreciated.

You would not be able to get the blue light to stay on if the battery was the issue. That being said, the batteries are probably still shot if you haven't charged them in 4 years.

 

[karikatourea]

Update, in case someone runs into a similar issue in the future.
The 3ds hacks guide has a discord channel I asked there too and they were able to point me in the right direction.
And that was the direction :
https://3ds.hacks.guide/a9lh-to-b9s.html

I followed the guide, and now they both turn on and boot. Apparently it takes more than a messed up backup to brick them.
Weirdly enough the batteries are fine too, they last more than 2 hours of usage, which is pretty great considering they haven't been charge in four or more years.

And I'm feeling all giddy and full of gratitude because I got help from random strangers on the internet and thanks to them the 3ds are back from the dead, up and running great.