My Xperia S which I bought in August 2012 doesn't boot anymore. A few weeks after I bought it, I unlocked the Bootlader and installed custom Kernels and ROMs and it worked fine all the time. I was on KA 22.1 SSpeed and Advanced Stock 17 and wanted to try something else, so I installed XZXperience 2 and the Elite V2-Kernel.
Well, after that, the phone worked fine but I noticed some heavy battery drain. Charging took waaay longer than usual (full charge about 4 hours with the plug) and the drain was immense. BetterBatteryStats showed me a Deep Sleep of 98 % while I lost about 15 % of battery life in ONE hour, that can't be somehow. The phone however worked still fine.
So I decided to flash the Advanced Stock Kernel again but the drain didn't stop, it was as before. I thought that the Battery Stats are maybe corrupted, so I let the phone discharge itself completely (didn't take long) and wanted to charge it fully. When I plugged in the charging cable, the first unusual thing was, that the red light appeared instantly upon connecting. Normally it would take a second or so. The second thing is, there was no logo, no battery symbol, just nothing but the red light when I plugged the cable in.
I slept a night and after I woke up, I disconnected the cable and wanted to start the phone, but nothing happened. Still, the only thing the phone does, is lighting red, when it's plugged in. Fastboot or Flash-Mode don't work, the computer doesn't recognize anything.
So...what to do? it appeared after I flashed the new ROM and Kernel, but I don't think it has something to do with them...the drain was also there with the Advanced Stock Kernel. Although I must say, that I often had flashing errors, often the device said something like:
format_volume make_extf4fs failed on /dev/block/mmcblk1p2
To me, it looks like the battery has a deep discharge and is dead, but I don't know, what could I probably do before sending it in? If the battery is dead the warranty should still be there, even with the unlocked bootlader, am I right?