I have a Vizio D55-F2 with a darkened top half that appears exactly like the picture in the original posting. I disassembled the panel and replaced all defective LEDs, some of which fail open causing an entire strip to go out while others fail shorted allowing other LEDs in the strip to continue working. I tested all the strips before reassembling only to find the problem remained. I then began looking at the signals from the backlight PWM controller and saw that the darkened top strips were actually being PWM’d while the bottom half was full on. By luck, I disconnected the bottom strip’s 58V supply as a test and all other strips came on and, even at 50% duty cycle, it appeared to have a nearly uniform brightness. The darkened state also appears to stem from a possible power up test because the bottom LED row did not light when reconnecting the 58V supply while powered on and it appeared to be no PWM signal for that row as if it had been disabled. The 58V supply is from a very noisy switching circuit and I...

It is more than likely not the battery, but that it is 'bricked' due to corruption of the boot-up firmware. Many people have had the issue, including myself, and resolved it by the methods at this link: http://rootzwiki.com/topic/38786-tpdebrick-v004/page__pid__1093281 If this works for you, then thank all the people who worked to develop a solution especially 'jcsullins'!