Opera Slams Microsoft Over Browser Battery Test, Claims It Can Offer Better Battery Life Than Edge

3 days back, Microsoft revealed a series of tests conducted on various laptops and measured the average battery life and power consumption in milliWatts for 4 browsers which include Edge, Opera, Firefox and Chrome.

The Microsoft test was run on Surface Books with identical hardware and concluded with Edge being the last to turn off and having around 7 hours and 22 mins battery life. In second place we have Opera with 6 hours and 18 mins, Firefox secured third place with a little over 5 hours while all time favorite(pun intended) Chrome lasted a mere 4 hours and 19 minutes.

However the test didn't go well with Opera. The company claims that Microsoft used a beta version of their browser which many people wouldn't use plus a couple of options had been enabled. They went as far as to publish their own study and comparing the browsers. A graph can be seen below plus a video on battery saver feature:

Opera is not impressed since Microsoft didn't exactly specify the version of the browsers. However they claim that Opera was tested with it's battery saver on.  They also went as far as to link The Wall Street Journal's article claiming Edge is the most power efficient browser. For reference you can see Microsoft's video below too:

Here is an in depth technical analysis for Opera's backlash and Microsoft's claim. Despite differences, both of them seem to be agreement of Chrome being the worst browser for battery saving.
What are your thoughts on this? Which browser do you think is more power efficient?