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Battery full capacity less then desiged


New Member
Just bought Surface Pro 2 a week ago, and so far I am very happy with it.
But the battery never reaches the full designed capacity of 42,000mWh. It is always at about 40,800 mWh when fully charged, and I am getting about 7 to 8 hour usage.
If a complete run-down of battery can help boost the capacity, how do I do it? The surface pro shuts itself off at 5%.
Thank you.


Well-Known Member
Never a good idea to completely run down the battery as that will shorten your batteries life. Going down to 5% is low IMO. And if your getting 7 to 8 hours, that is good compared to what others are getting, I find people are focusing/worry on small things that really shouldn't matter.


Active Member
I find a fair amount of variability in that powercfg reading, ranging from 39,000 to 43,000. If you're somewhere in that range, you're probably good. It might depend on the ambient temperature at which you charge at since that will affect the battery chemistry.


40800 is a good value and 7-8 hours is a terrific value! Don't bother if it would last longer if it reached 42k. Battery capacity isn't exact science.


Well-Known Member
Battery capacity is normal. It is an estimate, and the moment the battery is produced, the battery itself start oxidizing. So reaching the max theoretical value is impossible.
Your battery life is normal.

If you want to see how far you can push it. If you turn off Bluetooth, and Wireless. You set the brightness at 0%, and you are fully charged. The system is under Power Saver, where you limit the max CPU to 30% or 0% forcing it to 750MHz, you turn off the back light of the keyboard, no USB device attached, close all programs, and you wait a moment for Windows to update itself to this current usage (takes several minutes), then you should get ~12h of battery.


New Member
As long as 40800 mWh is a good number in average, I will keep my new SP2 and start enjoying it.
Indeed 7 to 8 hour is more than enough for daily note-taking in OneNote, which is the main reason for me to buy the SP2.
Thank you all.