Haswell macbook air 13 inch battery question...

So i got myself a macbook air 13 inch with haswell i5.... apple claim battery is capable of giving 12 working hours.
I am no fool , I do realise it is under certain circumstances... however, when I have my macbook air charged to 100% unplug it... have screen brightness to 100% and downloading some update on steam , it says i have 5:42 hours left of battery runtime... can 100% brightness and downloading something in background decrease the battery by 6-7 hours ???

I also noticed that the time is 100% true... it changes all the time for when the battery percentage is going down... like at 60% it will say 6 hours left... and i have changed nothing... even though at 100% it was 5 hours and 42 minutes...

should i be worried or this is normal ?

 

Battery life indicator refreshes not every 1 second.

Your laptops power draw is different in each second, mainly because of the CPU Turboboost that adjusts the clock all in real time - all the time. Even if the laptop idles, Turboboost can bump the clock for 2- 3 seconds, because of other program/s in the background needs to do something....

Yes, LCD on max brightness can reduce battery life dramatically, this is the most power hungry element of every laptop, also, WiFi is second in power hungriness just after LCD. Using both to their full potential EG max brightness/heavy downloading/browsing will decrease battery life, in some cases, yes, by way more than 50%

 

thanks for the explaining , guess apple should advertise this as well
don't know many people who use 50% brightness when browsing... or am i wrong..

 

about 75% here.

 

Depends on the lighting. I use around 25% a lot of the time because I like darker rooms.

 

is there some sort of test that can be done , to test the battery on my macbook air ?