The Myth of Leaving it Plugged In

The aged old myth of leaving your laptop plugged in forever and a day remains strong even today.

Many people claim that this is an old adage that doesn’t apply to modern Li-Ion (Lithium Ion) batteries, however there is just as many people who disagree. Even Apple agree with an official statement on their site about not leaving your laptops plugged in all of the time:

However, an article on the Dell website doesn’t recommend the same thing – In actual fact it neglects to comment on what you should do once your notebook is fully charged. HP even circumvent the topic in their article.

At work I have a Dell Latitude D630 with the Extended 9 Cell battery. When I first got the laptop it was fantastic – About 5.5 hours from a normal cycle or about 6.5 hours if I went hardcore on Device Manager and disabled all of the hardware like the fingerprint reader, DVD drive, modem etc.

The laptop during the day is attached to a Dell docking station and used a desktop with two screens and a keyboard and mouse. In the evenings I use the laptop for personal bits and bobs as well and keeping an eye on my email etc. In the evenings I charge it and then unplug it once it’s fully charged.

I’ve had the laptop about a year now and it was new when IT gave it to me, however over the last week Windows has been warning me that I should consider replacing my battery. No this isn’t Microsoft it cahoots with Dell and HP etc, because Windows tells you what it gets told by the output data from the battery. As it stands the laptop lasts less than one hour on battery.

This is a perfect opportunity to use one of the new features in Windows 7 – The Power Efficiency Diagnostics Report, or Energy Report shall we say.

Besides from information like the power settings of the machine, problems with hardware preventing standby and background processes consuming excess processor time, this report shows you some excellent data on the battery, which makes it perfect for IT departments to run if a user complains about poor battery life and allows you to determine if it’s the battery at fault or an application or an environmental condition.

To access the report, run the following command:

POWERCFG –ENEGERY –OUTPUT %UserProfile%DesktopEnergy.html

This will output the energy report to your desktop. This needs to be run from an elevated command prompt to warn you in advance.

The application will gather the data for 60 seconds, during which time you should have no user or foreground applications running, so that means signing out of an closing Windows Live Messenger and anything else you may have open.

Once it’s finished look your desktop for the Energy.html file.
In this example I’m interested in the Battery Information which is near the bottom. Here is the output from my laptop:

Battery: Battery Information

Battery ID: 2693SMPDELL DU1398
Manufacturer: SMP
Serial Number: 2693
Chemistry: LION
Long Term: 1
Design Capacity: 86580
Last Full Charge: 33089

So as you can see, my battery has a designed capacity of 86580 but the last full charge only gave it 33089 units which is 38% of it’s maximum.

To me, this is pretty much proof that leaving the battery plugged in to the mains when you don’t need it is damaging the battery. Perhaps not due to the charging process but perhaps due to the extra heat generated, but either way it’s not good for it.

Once I get my new battery I’m going to run the report on the brand new battery to see how much of it’s maximum capacity it holds out of the box. I’m also going to experiment with the old battery to see if I can use an old trick with the fridge to increase it’s life again.


Richard works as a Cloud Consultant for Fordway Solution where his primary focus is to help customers understand, adopt and develop with Microsoft Azure, Office 365 and System Center. Richard Green is an IT Pro with over 15 years' of experience in all things Microsoft including System Center and Office 365. He has previously worked as a System Center consultant and as an internal solutions architect across many verticals. Outside of work, he loves motorbikes and is part of the orange army, marshaling for NGRRC, British Superbikes and MotoGP. He is also an Assistant Cub Scout Leader.

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