I have no idea. My phone dims depending on the light. If it's really bright, the phone gets really bright. If it's dark, the phone dims depending on the amount of light available. Regardless it wouldn't be a Microsoft issue, it's an OEM issue. The OEM deals with the display and how it acts.
As for the battery, I doubt you will see 2 days heavy usage on any smart phone with a comparable battery. It just won't happen. I can get a day with heavy usage on my Lumia 920. Not 24 hours, just the day. So 8AM to 8PM basically. But, I'm in an area with LTE service. And if you're only getting a couple bars of singal on LTE, well, expect your battery to drain even faster. I have WiFi, LTE, Bluetooth, and NFC always ON. I just charge my phone every night.
Also, kill the battery some night and then leave the phone off for a while. Don't plug it in right away. An hour or so later try to power on the device. I did this and to my amazement the device powered on and showed 20% battery remaining. The damn thing lasted through the night and into the next morning after some heavy usage. I gave it a full charge. After that, the battery percentage was much more accurate. The phone lasted much longer. This was about two weeks after I got my Lumia 920.
Some days, when I rarely use the device and I'm in an area with good reception, I can get days out of my battery. I've managed to get 4 days of light usage on a charge. You can get more on standby with minimal usage. But who buys a smartphone and doesn't use it?
If the display is acting up, bring it to your mobility dealer. Have them try the same thing with one of their devices. See if it happens with another device.