Whether it's a laptop, a tablet, or a smartphone, battery life estimates always seem like they're totally wrong. How-To Geek explains why.
While this might seem obvious, battery estimates tend to be off because they can't predict the future. All the software can do is look at what you're doing at that exact moment, then attempt to estimate how much battery life is left assuming you continue to do exactly the same thing for the rest of time. How-To Geek explains:
For example, a laptop might estimate ten hours of battery life if you dim its display and browse the web. Crank the display brightness to maximum and launch a demanding PC game, though, and the estimate might become two hours... This estimate can also fluctuate based on the work your computer is doing in the background. For example, Windows might be installing updates -- that will use more CPU resources, drain battery power more quickly, and lower the estimate. Even if you're just browsing the web, some websites -- especially ones with video ads -- use more system resources than others.
It's pretty obvious once you think about it, but it's likely not something all of us think about often. Head over to How-To Geek for more details.
Why Is My Battery Estimate Never Accurate? [How-To Geek]