[Xperia Z Q&A, Help & Troubleshooting] emiglet:
TL;DR, phone dropped on the floor, flat on screen, no damage except for a ratling noise in the bottomleft corner of the phone where the vibration is, which i didnt notice until after i dropped the phone. Charged a few times, but refused alot of the times, now it doesn't charge anymore.

Right now, every time I connect the phone to a charger, it starts showing the red LED, vibrates non-stop, until after 15 minutes it stops vibrating, giving fast pulses of vibration to slower pulses, and for the last 30 minutes, while connected to my laptop, it gives off a medium-soft vibration every 5 seconds, slowly degrading to every 20 to 30 seconds after half an hour.Interestingly aswell, it vibrates very strong for the first 30 seconds, than vibrates normally for the next 15 minutes before it stops vibrating. It's very consistent in this behaviour

Full story:

I bought the phone April 2013, and it was working fine until somewhere November 2013.

The percentage of the battery wasn't consistent at all. It was jumping every few seconds between e.g. 70, 73, 67. 60, 70, 71... sometimes it fell down to 23%, next thing happens, the system gives me a pop-up "Shutting down". It shuts down normally, I boot it up normally, and that's pretty much how it went. I made backups, continued with the use. Sony Customer Care tells me that I should update it/reset to factory settings.

I connected the phone for an update, and as the phone is updating, it shuts off because of the problem stated above (even with cable...).

Phone bricked, sent it April 2014 for service because I had a different phone and I was too lazy to send it back.

3 weeks ago I got my phone back, fully working (Yaay, right?). 2 weeks ago, I was sitting, doing my natural business and put the phone on a shirt I had at the window. The slippery phone pretty much slides from anything that's soft and has the slighest angle, so my phone starts sliding super slowly, and 10 seconds later it hits the floor screen down.

It fell so perfectly flat on the screen, on the perfectly flat tile, that the screen is still perfectly clean and there is no sign of damage. But, the phone was off (it was on before it fell). Shocked, I boot the phone, and it boots, with a sense of relieve I continue using it. However, I did hear a rattling noise from the bottom-left corner where the vibration is located (vibrator... hihi).

Here's where the new problems start...

Day 1, I shut down my phone on 15% so I save battery for later, for pics and such. Suddenly when I try to boot it, it tells me the battery is too low (a few red led flashes). 1 hour later, it turns on with only using the power button.

Day 2, I use the phone normally, phone drops to 2% and just waited until it would shut down by itself. It didn't, stayed like this until 1%, to where I have shut it down and plugged into the USB cable.

Day 3, The phone didn't show any LED, and when I would reconnect it to the AC charger, it would show the red led for about a minute and go off again. Phone stopped charging... Later I tried the car charger, still nothing. A few hours later I tried the car charger again and suddenly it started charging again to the full 100%.

Day 5, I had the phone in my pocket, and had to drive for about 60km. The phone was at 30%, and I found it to be turned off, showing me the battery is low through the red led. 60km was about 30 minutes, so I sensed something was wrong here. It didn't charge again, nor through PC or AC charger, not even the car charger.

Day 6, I tried the car charger, and again, it started charging, got it again to the 100%. I'm just browsing in the afternoon at 51%, and my screen turns black. I press the power button to light the screen, but it blinks 3 times red. I put the phone in the charger, nothing... Later that evening I put it again in the charger and left it for an hour, and the red LED finally showed! Well, the red LED was lit for at least 12 hours and the phone didn't respond to anything.

Day 7, It did vibrate 3 times when it tried the Power Button + Volume down, but blinked red again and no response.

Day 8, I started pressing the phone gently, and it started to vibrate on pressure. Pressing = vibration, release pressure = vibration stopped. What?? It could keep this up for about 5 minutes before it stopped.

For the last few days i try charging it occasionally, but the only progress that I got, is that the phone started vibrating non-stop when it was connected to a power-source, and the red LED was lit. First it would stop vibrating when I pressed the sides of the phone in a certain way, and just lay there silently with the red led. Now it just vibrates non-stop and there's no helping it.

Right now, every time I connect the phone to a charger, it starts showing the red LED, vibrates non-stop, until after 15 minutes it stops vibrating, giving fast pulses of vibration to slower pulses, and for the last 30 minutes, while connected to my laptop, it gives off a medium-soft vibration every 5 seconds, slowly degrading to every 20 to 30 seconds after half an hour.Interestingly aswell, it vibrates very strong for the first 30 seconds, than vibrates normally for the next 15 minutes before it stops vibrating. It's very consistent in this behaviour.

So, I found this thread:

http://xdaforums.com/xperia-z/help/hardware-fix-xperia-z-charging-booting-t2760911

I contacted Sony Support, they said there are no VOID indicators in the phone, as they will be able to tell if there has been a person in the phone. There's an unauthorized service nearby who can order OEM Xperia Z parts, so I doubt it they will notice. When I asked if I would still have warranty after the unauthorized service, but they would be unable to tell because he/she used OEM parts, they simply said "You will lose your warranty", because they probably couldn't contradict it.

Judging from the symptoms, do you assume it's a dead battery, or could it be someting completely else? It dropped, something rattles and it gave me a hard time charging it, but still it worked. Note that I used the phone intensively for 6 hours before the screen went black at 51% (fairly the same as using your phone to 0% and suddenly it just turns off).

I don't feel like losing my phone for 30 days again, nor getting my data wiped (ALWAYS BACKUP, I was too stuborn not to, even though I had plenty of chances...), and i'd rather just pay a few bucks to get my battery replaced (about 50 dollars). The time and data is worth it, there is a shop servicing Sony Xperia's after warranty, so at least someone who knows how to fix these phones.

The back-cover is not water resistant anymore as the glue detached because of the excessive heat from the processor. So I might just open up the phone and see whats going on anyway?