QUESTION The battery life on my laptop seems to be much worse than it was originally. I've had it plugged into the mains and turned on all day and night pretty much since I bought it, but sometimes I do take it out with me and it does seem to be considerably worse than when I bought it. I know that the battery life will vary depending on what I run on it, but how can I tell whether it's a software issue or a problem with the battery? (For Mac users, see: How to optimise battery life on a MacBook: Make your MacBook battery last longer.)
HELPROOM ANSWER Since Windows 8, there's been a battery usage and performance report built into the operating system. You can use this to measure the capacity of your battery compared to its 'design capacity', which is the capacity you should expect from a brand new battery of the type you're using. This capacity is usually rated in Watt Hours (Wh) and is a statistic we quote on all our laptop reviews. With use, the actual capacity of your battery in Wh will decline until it needs to be replaced.
The battery capacity history function, built into Windows 8, will compare your battery's actual capacity against the design capacity over a period of time, so you can see how well it is performing. If the measured capacity has dropped significantly, it's probably time to buy a new battery.
It's also worth noting that leaving a laptop plugged in and turned on for extended periods can cause the battery to deteriorate more quickly. We'd actually recommend taking it out and putting it back in when you need it (allowing enough time to ensure it's fully charged).
Generate laptop battery report
To generate a battery report, open up a command prompt by pressing Windows+X and selecting 'command prompt'.
At the command prompt, type: powercfg /batteryreport /output MYFOLDER\mybatteryreport.html
(Where MYFOLDER is the full path name to the folder where you would like to save the report.)
Now press Enter. This will create an HTML file called mybatteryreport.html, which you can read in your favourite browser. Note, this only works on devices fitted with a battery.
Try it on a desktop computer and you'll just get an error message. (See also: How to improve smartphone battery life: 10 tips and tricks.)