Notes on comments.
Welcome to our blog dedicated to the engineering of Microsoft Windows 7
Over the past week we have seen a little bit of blogosphere activity regarding Windows 7 and batteries, specifically the new Windows 7 message “Considering replacing your battery”. Since this is related to the engineering of Windows 7 we’re going to use this blog to provide an update to people. As we have talked about many times, we have a relentless focus on the quality of Windows 7 and we take seriously any reports we receive that indicate a potential problem that could result in a significant failure of the OS. In a previous post we talked about the steps we take when we receive a bug report, in particular when we start to see several reports that appear to be the same. For the past week or so we have been diligently working through these steps and more to see if there is anything in Windows 7 we need to address regarding this issue. At this time we have no reason to believe there is any issue related to Windows 7 in this context.
Several press articles this past week have drawn attention to blog and forum postings by users claiming Windows 7 is warning them to “consider replacing your battery” in systems which appeared to be operating satisfactorily before upgrading to Windows 7. These articles described posts in the support forums indicating that Windows 7 is not just warning users of failing batteries – as we designed Windows 7 to do this – but also implying Windows 7 is falsely reporting this situation or even worse, causing these batteries to fail. To the very best of the collective ecosystem knowledge, Windows 7 is correctly warning batteries that are in fact failing and Windows 7 is neither incorrectly reporting on battery status nor in any way whatsoever causing batteries to reach this state. In every case we have been able to identify the battery being reported on was in fact in need of recommended replacement.
Using all the tools at our disposal including contacting customers reporting this issue on forums, customer service communications, partnerships with our PC makers, and of course the telemetry in Windows 7, we have been monitoring reports and discussions regarding this new feature, trying to separate reports of the designed behavior from those that might indicate an issue with Windows 7. In the latter cases we are trying to understand the scope of applicability and obtain hardware on which to reproduce a faulty behavior. To date all such steps indicate that we do have customers seeing reports of battery health issues and in all cases we have investigated Windows 7 has simply accurately detected a failing battery. Before I go into our status on this particular issue, we should review the details behind this new feature.
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. A quick check of mainstream laptops will show that batteries usually have a warranty of 12 months, which is about the length of time when statistically we expect to see noticeable degradation (meaning that you start to notice the need to charge more frequently). Those of us that have owned the same laptop (or mobile phone, or music player, or anything else with rechargeable batteries) for a couple of years and taken it through regular charge cycles have no doubt “felt” the decline in battery life though we might have attributed to any number of factors since we did not have any information available to us otherwise.
Windows 7 makes use of a feature of modern laptop batteries which have circuitry and firmware that can report to Windows the overall health of the battery. This is reported in absolute terms as Watt-hours (W-hr) power capacity. Windows 7 then does a simple calculation to determine a percentage of degradation from the original design capacity. In Windows 7 we set a threshold of 60% degradation (that is the battery is performing at 40% of its designed capacity) and in reading this Windows 7 reports the status to you. At this point, for example, a battery that originally delivered 5 hours of charge now delivers, on average, approximately 2 hours of charge. The Windows 7 the notification is a battery meter icon and notification with a message “Consider replacing your battery”. This notification is new to Windows 7 and not available in Windows Vista or Windows XP.
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.
As mentioned, every single indication we have regarding the reports we’ve seen are simply Windows 7 reporting the state of the battery using this new feature and we’re simply seeing batteries that are not performing above the designated threshold. Below we’ll talk about the data we have to support this point of view. It should stand to reason that some customers would be surprised to see this warning after upgrading a PC that was previously operating fine. Essentially the battery was degrading but it was not evident to the customer until Windows 7 made this information available. We recognize that this has the appearance of Windows 7 “causing” the change in performance, but in reality all Windows 7 did was report what was already the case.
This data would confirm our point of view that we are seeing nothing more than the normal course of battery degradation over time. The transparency provided in this new Windows 7 feature produced a notice that previously was not available to customers and did so shortly after upgrade. This is the root cause of the urgency with which we’ve seen postings, but does not change the reality of the condition of the battery. We have no confirmed cases of new machines with the as-purchased batteries.
As we always say with regards to any reports on the quality of Windows 7, we are going to continue to be diligent and use all the tools at our disposal to get to the bottom of a report that has the potential to require a code change we would distribute to customers. We are as certain as we can be that we have addressed the root cause and concerns of this report, but we will continue to monitor the situation. In particular, we will continue to have focused communication with our OEM partners as they monitor their customers and PCs over time.
Finally, if you believe you are receiving this error and your battery is new or believed to be in great shape we would encourage you to report this to us or your original PC maker. You are welcome to send me mail through the contact form on this page, use the TechNet forum, the Microsoft Answers forum, or visit support.microsoft.com where you can get additional information about how to contact Microsoft assisted support in your region.
Can you at least check Designed/Current capacity on your battery? That would really help all of us a lot. I haven't tried the link above but if you like cpu-z, you would most likely like CPUID Hardware monitor.
If you have another OS, then it is absolutely better to use CPUID HWM on that OS too with the exact same battery and see the results.
Righto, checked, and in my case, value in the Design Capacity field matches what it should be in actual fact.
New battery time then... :\
Just to be clear, you're comparing <b>Designed Capacity</b> against <b>Full Charge Capacity</b> (not Current Capacity, my bad...)
If your Full Charge Capacity is indeed considerably lower than its designed, then really do consider replacing your battery.
If you have a (null), zero, or absurd Designed Capacity (as someone pointed out could be a cause) and you're getting erros from W7, then truely W7 is at fault.
Wy when Windows 7 turn off my computer because the battery is low to the critical stat 1%, I am able to start with Windows XP and work 15min more at 0% stat?
Can we set Windows 7 to do nothing when the critical stat is arriving?
I checked my battery states using the Lenovo power manger which also reports health state of the battery. The Lenovo tool states good on two of them and poor on the other two. Those reported as poor are recommended to be replaced by as well Lenovo tool and Windows 7. Comparing full charge and design capacity is the best way to determine the health state of a battery. I just bought a new battery which has a slightly higher full charge than design capacity. I frequently checked my battery health using the power manager in former times and also noticed a degradation of the full charge capacity over the time which is normal due to the chemical processes in a battery.
The notification to replace the battery itself is good thing since a highly degraded battery might also cause data loss in case of an immediate power outage. However since there seem to be issues with batteries in the field where the measures are not set properly in the batteries or somebody knows that a battery is old and poor and is properly not willing to replace it, an option to disable the warning might be a feasible solution to get rid of the nag.
The ability monitor battery health (not just current charge) is something the OS should be providing, and I'm glad it's now included in 7. For a while now I've used BatteryBar (http://osirisdevelopment.com/BatteryBar/index.html) which has exposed this information to me. My laptop at the moment is fully charged with 45,577 mWh of its designed 86,580. That's almost 50% wear over the 2 years I've owned this computer. Removing the FEATURE as DanLee81 suggests isn't the answer. If the error message is too vague it should be reworded, and once it's warned the user it should stop nagging. Perhaps a configurable threshold or ability to disable the check entirely (by means of a registry setting, I assume) would be good, since Windows 7 is all about user choice.
I obviously don't know specifics about the people who are experiencing this problem (I personally have not experienced it on any of my PCs), but what Steven from MS posted it about makes sense to me, especially given what I know of batteries. I work for a video production company and we have several batteries we use to power our fleet of cameras. They ALWAYS discharge whether they're in the cameras, in the chargers or sitting on a shelf or in a bag. Some of the batteries don't hold a charge for longer than about 5 minutes now, while another we purchased at the same time works for almost an hour. There are a lot of variables with batteries, and even so-called "new" batteries may not operate at full capacity if they've been sitting in some warehouse for months or years.
Just my $0.02
If your designed capacity value is zero or absurdly high then your battery is likely at fault for providing wrong information to your laptop.
It is my perception that in the past month or two some change to Windows 7 has significantly reduced battery life on my ASUS Eee PC 1000HE. Before this "update" it ran for 6-8 hours. Now 4 hours is the best. I do not believe the battery's capacity declined this quickly. I believe it something that Microsoft did in a Windows 7 patch.
Wow you are alive. We had no indication of that. Never thought you guys really checked in the forums. Hope Windows 7 SP1 includes dozens of fixes for annoyances still remaining since Vista RTM.
You only defends for Microsoft. Speechless.
While we're on the topic of power management, I'd like to be clarified why the damn OS doesn't even get switching power plans right. There's no automatic power plan switching and "Balanced" is a fixed plan so you have to open the Control Panel everytime to switch between High Performance and Power Saver plans. You've oversimplified and streamlined the whole scenario. Vista reduced the number of plans to 3 and now Windows 7 to 2. Maybe Windows 8 will show just a single plan. Why is user experience so poor. MS says they've done UI experience research so is this all you can do?
Why does Windows 7 not show time remaining like XP? No info on battery name, manufacuturer and type of battery? Why do I have to run Mobility Center as admin instead to see the brightness tile?
My problem with this is very strange. Only sometimes I got this error message, when my HP Tablet tc4200 was running ONLY on battery.
It suddenly tells me my battery is dead/corrupted or I've removed it.
While stating this Windows 7 Prof. is still running BUT the system crashed somehow: I can move the coursor and click on the Windows-button or other icons, but they won't open atall.
I even can't porperly shutdown my PC.
After a hard reset of the PC I can boot back into Win 7 and can continue to work until the battery is at 5%.
SO this battery is 3 years old, but it can run 4hours, often without windows crashing like I descriebed. But it is still an annoying issue!
Any solutions? Going back to Vista?
If ACPI is reporting an incorrect value for design capacity then that's an issue for the OEM to fix their BIOS, which is what sets up the ACPI tables. Similarly, Last Full Charge Capacity can be erroneous if the BIOS changes the value at the end of a partial charge rather than fully recharged. It's worth checking for BIOS updates that could correct this.
There is a way that software can damage batteries: high discharge rates. You should be able to notice this if the system's cooling fan runs more often than you would previously expect, when running on battery. A computer upgraded to Windows 7 might do this if you have something left over from Windows Vista that is not compatible and which therefore runs more frequently. More likely though is that you're using the computer differently from how you used to. Check for high CPU usage and download Process Explorer to check for high amounts of time spent handling interrupts and DPCs (if there are, check for new device drivers). Heavy disk usage draws a lot of power. The screen backlight is usually the heaviest current draw if the CPU is idling - try turning it down a bit.
Windows Vista upgrades take a very long time. Ensure you're on AC power all through the process.
Lithium-ion batteries prefer shallow, slow discharges. Try not to run the battery right down but instead only use the laptop as little as you can.
@Dave Brown: there is a problem with your battery or charger. Even with very high discharge rates it should last longer than 30 cycles. Discharge at 1C (the 'amp hour' rating on the battery) should go up to 500 full discharge cycles before dropping to 80% capacity.
Laptop batteries are usually 'smart' with an embedded safety circuit that tells the laptop how to charge it, so it's more likely to be the battery's fault.
@Timo: you probably have a bad contact that is causing interruptions in power, something that computer hardware isn't designed to handle. Dynamic RAM must have each bit of storage refreshed many times per second - if this doesn't happen data read back from RAM may no longer be what was written. Software is completely at the mercy of the hardware functioning correctly.
Thank you for this very insightful article Steven.
I am using a 13.000 mAh battery on my Asus EeePC 1000H with Windows 7 Home Premium. The battery is fine, just 97.000 mWh left (perhaps 1-2% wear level). But Windows 7 tells me that I have to replace the battery. I helped myself by disabling the annoying battery popup message.