Laptops now outnumber desktops in sales and that trend is only set to broaden in coming years.  With the majority of customers now using laptops, anything on an operating system level that affects laptop users is becoming increasingly important.  Thus, when reports popped up that Windows 7 was erroneously telling users to replace their batteries on perfectly healthy notebooks, many took note.

Microsoft's Windows President, Steven Sinofksy, has fired back in a long post in which he defends how things currently work, stating that his staff have found no bugs.  He writes, "One of the most obvious components of PC battery life (the runtime you get on battery power) is the battery itself. PC batteries inherently degrade in their ability to hold a charge and provide power (as is the case for all rechargeable batteries). The cause of this is complex and includes irreversible changes in battery chemistry, and increased internal resistance among other things and those in turn are dependent on the design and manufacturing of the battery. This degradation translates into less battery life for the user over the life of the battery in the PC.  Ultimately, batteries must be replaced to restore an acceptable battery life."

Mr. Sinofsky says that it warns users to change their battery whenever it is operating at less than 60 percent of its original capacity in watt hours.  He explains how this works, writing:

PC batteries expose information about battery capacity and health through the system firmware (or BIOS).  There is a detailed specification for the firmware interface (ACPI), but at the most basic level, the hardware platform and firmware provide a number of read-only fields that describe the battery and its status.  The firmware provides information on the battery including manufacturer, serial number, design capacity and last full charge capacity.  The last two pieces of information—design capacity and last full charge capacity—are the information Windows 7 uses to determine how much the battery has naturally degraded.   This information is read-only and there is no way for Windows 7 or any other OS to write, set or configure battery status information.  In fact all of the battery actions of charging and discharging are completely controlled by the battery hardware.  Windows only reports the battery information it reads from the system firmware. Some reports erroneously claimed Windows was modifying this information, which is definitely not possible.

Despite this assurance, though, many customers still say Windows 7 is saying they need to replace their battery on new machines or machines with little battery wear.  The response section of the blog was inundated with angry replies from users experiencing such issues.  

Among the models that reportedly have had this problem are the Asus Eee PC and certain Acer Aspire models.  Some users have reported that Windows 7 is shutting down their computers when they still have battery life remaining.  And other users have noted that they can take the "failed" battery and put it in a non-Windows 7 machine and it will charge just fine.

Given the amount of complaints and uncertainty, Microsoft hopefully is investigating this issue further, however, it clearly appears to currently feel that there's no issue at all, despite its customers' testimonies.