Here's a bit of info you might need:
I've had my device for about a year now and only ever dropped it from really low heights, which never caused any issues (except for a few breaklines on my screen).
My device has been rooted and I've installed a custom ROM (I can't recall which one exactly, but it never caused any problems and just made things better.
Starting about 6 months after I got the device, it started sometimes lagging a little.
Now just the night before, I plugged in my headphones, put on some music and went to sleep (as I do every night). The phone was not plugged into the charger. Once I woke up, I wanted to take a look at my phone to see the time, but it was just a black screen. I think it probably doesn't have any power left and plug it into the charger. Nothing happens. No icon, no little flashing light; nothing. I plug it into the computer and my computer doesn't recognize my phone to be connected, so it's not my display which is broken.
Now I think the problem must lie in the battery, but I'm not sure, since I can't take the battery out. So here's what I need to know:
1. How can I check if it's actually the battery that's broken?
2. Is it possible to open the phone and take out the battery somehow?
3. Is there a way to fix this? If so, how?
Keep in mind that I don't have warranty on the phone anymore, so I can't just send it somewhere to get it fixed.
Any help would be greatly appreciated! Let's hope for the best