FAQ: BatteryBar's time estimate is different than Windows

[Chris]

A common question about BatteryBar is why the time remaining estimate is different (often significantly lower) than the Windows report time remaining.

BatteryBar calculates time remaining in a completely different way than Windows. Windows makes a very simple calculation of dividing the capacity remaining by the current discharge rate (you can see these values in the BatteryBar popup). However, discharge rate is constantly fluctuating, so you'll see time remaining estimates from one minute to the next change by up to an hour, just because something at that moment was using more or less power. Just because Windows says 10 hours remaining when you're at 95%, doesn't mean that you won't get to 0% until 10 hours later, because it doesn't keep track of the historical usage pattern of your battery.

BatteryBar keeps track of the actual amount of time that you battery lasts from one percentage point to the next and continually updates that profile as you use the battery. The time remaining is then reported as the average amount of time your battery has historically lasted from that point. The time remaining value is also adjusted based on a ratio between your average (historical) battery life versus how much power you're currently using.

If you wish to test the accuracy of the time estimate, I suggest that you take a notebook and write down the current percent remaining and the reported time remaining. Then use your computer normally for 15 minutes (don't just let it idle, it'll change the time remaining estimate) and write down the current time, what percent you are at and the time remaining. Do this during a normal usage session. You should see that BatteryBar's time remaining estimates change by almost 15 minutes for each line you wrote down. If you see that 15 minutes later, BatteryBar's estimate has only changed by a few minutes, then it may have incorrect or incomplete battery profile data.

You can see exactly how BatteryBar calculates the time remaining by right-clicking on BatteryBar and choosing "Battery Profile Graph". Choose your battery and power scheme (if you have it set to keep a separate profile per power scheme, otherwise choose None). You can click on Browse Percents and move the slider around to see the estimated time remaining at each percent remaining.