Do you ever feel like the actual battery life on your notebook never quite equals the information that appears in promotional material? For example, you may see “up to five hours,” but actually get about half that.  Well, you aren’t alone.  I hear it all the time, and if you do a quick Twitter search on the topic, you’ll see lots of discussion.

I can assure you that no devious plot exists to mislead you. It really comes down to three simple factors.

#1: Measurements are best case: Like a car’s “highway miles per gallon” which gauges the best case (cruising at a sustained speed for an extended period without stop-and-go driving), notebook battery life is typically based on MobileMark® 2007. This benchmark primarily measures battery life while the notebook is doing nothing – not even wirelessly connecting to the Internet. A “city-driving” equivalent of notebook battery life doesn’t exist…yet.

#2: Different strokes for different folks: Notebook users are different; we all use notebooks differently, and therefore will see different battery durations.  Some watch HD web videos on YouTube, some may just do email, and some play more games than others. ALL which will mean varying battery life.  You can see this data from AMD here that shows the phenomenon.  This even shows that battery life under system use can even vary by component manufacturer.

#3: Battery life varies over time: The longer you own your notebook, use it, charge, and recharge, over and over again, the more the battery loses its effectiveness.  So theoretically, your longest battery life will be on the first day you crack open the packaging.  See all the people selling new batteries for old notebooks?  Some even say, battery life is variable with heat.

So what should a consumer like you do?

• Grade battery life on a “curve”, let’s say 60%. If the label says 10 hours, my guess is it’s probably only about 6 hours in real use.  (UPDATE: this isn’t always linear, so be very careful with this.)
• Ask your retailer and systems providers to provide the “city miles per gallon” or using the tried and tested cellphone analogy, “talk-time”. They all have web sites and when all else fails, you can ask them over Twitter.

I may have not added back 40% of your battery life, but hopefully you know why you only get 60% of it!

(This blog was originally published at the Technologizer web site. Updated with full blog June 8, 2009.)