I bought a used ASUS ZenBook 13 from a computer store two days ago. Before buying it, I checked the Windows battery report and saw a design capacity of 71 Wh and a full charge capacity of 68 Wh, suggesting roughly 95% battery health. After taking it home, I noticed corrupted-looking Windows files and that charging was stuck at 65%. A reset and cloud reinstall did not fix the issue, so I returned it to the store and asked them to reinstall Windows.
After bringing it home again, I generated another battery report. This time it showed a 68 Wh design capacity but only 42 Wh full charge capacity, indicating more than 30% wear. Battery life was one of the main reasons I chose this laptop, so the difference is worrying. Could reinstalling Windows or repairing corrupted system files cause the reported capacity to change, or is it possible the store replaced the battery? The newer report also shows what appears to be a generic battery serial number, which makes me wonder whether it is a cheaper third-party replacement. What should I check, and should I ask the store to replace or refund it?
3 Answers
A Windows reinstall should not physically reduce the battery's capacity, but the first report may not have been accurate. Battery readings can change after the laptop has been sitting unused, after firmware or driver changes, or after several charge and discharge cycles. I would not conclude that the battery was swapped based only on the two reports.
Check the battery model and serial number in the new report and in the BIOS, and compare those with any photos or records from before the reinstall. Also let the laptop complete a few normal charge cycles, then generate another report. If the capacity remains around 42 Wh, take the laptop back under the store's warranty and ask them to explain the discrepancy.
If you have no original report, proving a battery swap may be difficult. A generic-looking serial number can indicate a replacement or poorly programmed battery, but it is not definitive proof by itself. The battery's model, manufacturer, design capacity, firmware information, and BIOS listing are more useful than the serial number alone.
Take screenshots of the current report, record the battery identification details, and ask the store to inspect it in front of you. Since the machine already had problems when you bought it, requesting a repair, replacement, or return is reasonable regardless of whether you can prove intentional swapping.
For a used computer, a clean installation from official Windows installation media is generally preferable to simply using the existing reset option, since you cannot know how the previous installation was configured. That said, neither method should turn a genuinely healthy 68 Wh battery into a 42 Wh battery. The difference could be inaccurate initial readings, battery calibration, firmware reporting, or a different battery.
Back up anything important, test the battery over several cycles, and document everything. If the reported full-charge capacity stays far below the design capacity, use the store's return or limited warranty policy instead of trying to repair it yourself.
I did not save the original report, although two other people saw the earlier numbers with me. I will compare the battery details in the report and BIOS and let it complete a few cycles before going back to the store.