Seems to work fine here.
12" Rev B.
Battery charge seems to be 1% more than the Apple menu item.
Refresh hits the CPU (My Energy Saver settings are set for longest battery life though) and iTunes will stutter.
Seesm to pretty much match with:
ioreg -p IODeviceTree -n "battery" | grep IOBatteryInfo
But I guess that's what you are doing anyway?