I read that bit of advice about choosing html5 the other day and not only has it improved power issues it has made a huge difference to stability. I had noticed a lot of youtube videos on my last machine and on this new one crashing, since changing the setting its not crashing and you can scan through videos in almost realtime. Was the same on my stopgap Windows machine.
To think there was uproar when Apple announced they would not be suporting Flash on tablets and phones, judging by how poorly it seems to run on all pcs it makes perfect sense.
Back to OP, its down to brightness settings, browser, what you are doing etc.
Earlier I was getting 61% battery remaining 5hours 40, that was just using Safari to upload stock to discogs(music site) with brightness half way so I guess that works out at 10% per hour which is very decent. Ive now got the brightness up and have Firefox open also which is always more hungry and im getting an hour remaining with 29% battery left.
) But not sure how accurate the meter is though