Hi,
I had a similar problem of screen flickering while on battery power on my Asus TP550. I tried all different power settings on my laptop, but with no luck.
Over time the screen flickering got worst until one day my screen went completely blank (on battery power only) and I could only use the laptop when plugged in.
I decided to buy a £75 donor laptop off eBay that had a faulty motherboard, so I had all the parts available to me to correct the problem. After just a couple of minutes, I discovered it was a problem with the back light on the LCD panel and by replacing the LCD panel I was able to correct the problem.
I was able to test this before swapping over the LCD panel. I switched on the laptop (just using battery power), I switched on my iPhone’s torch and shined it through the back of the LCD panel and was able to see the desktop icons.
I swapped the LCD panel, and this cured this problem. I was also able to sell the parts of the faulty laptop on eBay to make back the costs of buying the faulty laptop.
I hope this comment helps someone as this issue was difficult to diagnose.