How can I get my laptop to tell me how much charge it really has?

June 7, 2007 4:27 PM

My laptop tells me that my battery is Critical, then it lasts for a further half hour! What is going on?

I've got a four year old Dell Latitude X200. The battery usually has 35-50 minutes of charge, but Windows XP tells me that it is Low (5%) after 15 minutes, and Critical (2%) after 20. A few days ago, I decided to test it, and it lasted a good 15-20 minutes beyond when my computer told me it was critical. I've done it a couple of times since, and still the same outcome.

Is there a way to "re-zero" my laptop to recognize how much charge my battery actually has left?

I realise that it would probably be easier to replace the battery, but I really can't afford one right now.

posted by cholly to computers & internet (8 comments total)

is your laptop reducing power consumption (dimmer screen etc) as the battery dwindles? I have a laptop that does this so, when it says :15 left what it really means is :15 left at current power consuming levels.
posted by edgeways at 5:12 PM on June 7, 2007

Laptops and other electronic devices cannot measure a battery's remaining power very effectively throughout the range of operation. Mostly this is because batteries behave nonlinearly - especially near total discharge - so it becomes some matter of guesswork as to what charge actually remains.

Further, closing down the OS and saving files may take a substantial amount of power (the hard drive must spin, and so on) or time. So the computer is set up to be fairly conservative on estimating power left so the user has time to perform these tasks lest file system corruption ensue.

All of that said, you might be able to tweak your power settings (In the control panel) to not issue warnings so soon. But the best way to fix this is to replace the battery since older batteries can be somewhat unpredictable in their ability to hold a charge - one day it won't at all.
posted by Pogo_Fuzzybutt at 5:37 PM on June 7, 2007

is your laptop reducing power consumption (dimmer screen etc) as the battery dwindles?

From what I can tell, no. However, the screen goes very, very dark (as in, non-readable) 15-20 after the battery goes critical.
posted by cholly at 5:52 PM on June 7, 2007

Have you checked the option to adjust power properties? On my Dell, I can choose what percentage left prompts me for low or critical alerts....
posted by keep it tight at 6:15 PM on June 7, 2007

if you can right click on the power icon in the taskbar and click "adjust power properties" then you can define "critical," etc.
posted by milestogo at 6:24 PM on June 7, 2007

go to the "alarms" tab to do so.
posted by milestogo at 6:24 PM on June 7, 2007

keep it tight, milesto go:

Thanks for your suggestions, but I've checked all that, Low is set for 5% and Critical for 3% - my problem is that my computer tells me that my battery is critical 15 minutes after I being using it, and then the battery will last for another 20 minutes. I just want to know if there is a way to change something so that the computer senses this level of power correctly.
posted by cholly at 8:11 PM on June 7, 2007

my battery is critical 15 minutes after I being using it, and then the battery will last for another 20 minutes

5 minutes isn't that much, and it sound's like you're running into the problem that Pogo described:

Laptops and other electronic devices cannot measure a battery's remaining power very effectively throughout the range of operation. Mostly this is because batteries behave nonlinearly - especially near total discharge - so it becomes some matter of guesswork as to what charge actually remains.

Here's a page from lifehacker on how to recalibrate your battery life.
posted by philomathoholic at 12:17 AM on June 8, 2007