Windows 7 - Consider replacing your battery
Windows 7 has native support for reading and tracking laptop battery life time. Before, additional software, like BatMon or NHC, had to be installed to read laptop battery info. Detailed laptop battery info is available for several years already originating from the Smart Battery standard. Though it seems Microsoft has released this feature while still in a steep learning curve. It sparked quite a bit of unrest among Windows 7 users – and not without reason it seems – it could have been easily avoided.
Windows 7 laptop battery life time test
Windows 7 released a battery life time test, setting the conditions for a Full Charge Capacity calculation – known as a Qualified Discharge. The test has no direct controls triggering the process at laptop battery chip level – it merely sets the conditions for a Qualified Discharge. The process is called "capacity learning" and measures how much energy comes out of a laptop battery from full to empty.
From a test perspective the Windows 7 battery life time test is “intrusive”, meaning the test influences the test result. After the test, battery capacity is affected by the test itself.
A non-intrusive test is the simple laptop battery test, which can be used when a laptop battery is discharged anyway – not particularly for the purpose of measuring the laptop battery life time. Precondition is a powered down laptop during full measurement or using a standalone laptop battery charger.
Windows 7 run time battery capacity tracking
Now next to the battery life-time test, it seems Windows 7 has a run time process tracking battery life time till it reaches 40 % of designed battery capacity. At 40 % Windows 7 users are confronted with the following message:
|Consider replacing your battery notification
Now immediately there are a few thing worth mentioning:
1. 40 % left is pretty high to consider replacement, laptop batteries are simply too expensive
2. Showing a red crossed out laptop battery is not nice – it's not damaged
3. Assuming values from laptop battery memory are correct is a big one
Because laptop battery memory is accessible for many years, it doesn’t imply values are reliable over a wide range of laptops and laptop batteries. Values come from deep down measured and calculated with embedded software running in the laptop battery and laptop motherboard.
|How battery capacity information travels from laptop battery chip level to windows 7 level|
As with all software development, mistakes are possible and in particular with embedded software. It’s specialist territory requiring rigorous testing to make sure values are reliable under any circumstance. To assume that’s true for the whole laptop and battery industry is a big one. The laptop battery gauge chip as well as the POST chip (Power On Self Test) run embedded software (firmware).
At least users shouldn't not be bothered with messages that could be based on erratic behavior deep down in a laptop battery chip (gauge chip) or anywhere in between (POST, BIOS, ACPI). Meaning Windows 7 software should filter for that and log unreliable info and disable run time laptop battery life time measurements.
Apart from all this – presenting a 40 % remaining capacity notification with a red crossed out laptop battery is not nice. It is not damaged. Laptop batteries are expensive and 40 % is not particularly the moment for laptop battery replacement. And especially not when the advisory could be based on erroneous information.
Windows 7 Consider replacing your battery information
For more information about the Windows 7 "Consider replacing your battery" warning:
Microsoft : Mobile Battery Life Solutions for Windows 7
Windows 7 forum : Windows 7 - Consider replacing your battery
Windows 7 Engineering : Windows 7 Energy Efficiency
Windows 7 Engineering : Windows 7 Battery Notification Messages
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