Excessive battery capacity loss
I have a ~1-yr old 13” Dell Inspiron 7000 with an internal 43WHr 3-cell L-Ion battery. I mostly use it as “desktop replacement" – it is connected to an external monitor and plugged into AC outlet 99% of the time. I’ve only logged about 90 hours of battery time in a little less than a year. However, I noticed the battery drained faster than usual the last few times I used the laptop in ‘battery-only’ mode. I ran the battery report in Windows 10 and it showed the battery capacity has decreased from 43WHr to 32WHr. I was shocked to see the new battery degraded by 25% in less than year, considering how rarely I use this laptop in ‘battery only’ mode.
I was thinking the battery might be defective but the Windows and BIOS battery diagnostics did not show any battery issues. I called Dell and their tech support guy told me 25% decrease in capacity could have happened due to me not using the battery enough/keeping the laptop plugged into AC for too long; as well as having the display brightness set to 100% and also my habit of putting the laptop in ‘sleep’ mode instead of shutting it down (I didn’t think it would impact the battery as long as the laptop is plugged in!)
Does what he said make sense? 25% capacity loss in under a year still seems unreasonable to me under these circumstances.
Can I request battery replacement as long as this laptop is still under warranty?
Many Thanks in advance for your advice!