My Dell Latitude E6540 sleep automatically when battery arrive 3%.
And when turn on an battery low level warning is shown.
How disable this?
You can go into Power Options > Change plan settings > Change advanced settings > Battery to disable automatically sleeping/hibernating at 3%, but that would risk your system just dying in the middle of your work, which could lead to data corruption, so I would not recommend doing this. 3% already does not give you very much margin for error, since sometimes the battery level isn't measured perfectly accurately. You should be finding power or putting your computer into hibernation before you reach that low to preserve your data. It's also very bad for laptop batteries to run them all the way to 0% on a regular basis, so if this behavior occurs often enough to be a problem for you, then you might want to do things differently in order to increase the longevity of your battery.
As for the low battery warning when you boot the system, usually it tells you right there that you can press a key to disable that warning in the future, but if not, then it might not be possible to disable.
I have already done this setup in Windows. But the notebook continues to sleep at 3%.
So, I think this is a notebook configuration. Maybe in the BIOS. I am sure?
I guess it's possible this is hardware-level behavior, but in that case if you don't see any BIOS settings to change it, then it's possible that this behavior is not configurable. I admit I've never intentionally taken my laptop's battery down that far, so I can't be sure. I've always hibernated it or shut it down sooner than that to preserve data, so I'm not sure.
But just out of curiosity, why do you WANT to let your battery go all the way down to 0% even if you'll risk losing data and definitely decrease the long-term life of your battery? I sort of understand wanting to use the battery capacity that you paid for, but on the other hand, you don't wait until your car is completely out of fuel before refueling or wait until your house is completely out of food before going to the grocery store, do you?
I do not want let my battery go all the way down to 0%.
I want let my battery go all the way down to 1%. That's enough time for me to plug in the charger (maybe because I have a 9-cell battery).
Anyway, thank you!
Ok, well as I said earlier, battery level isn't always measured perfectly accurately, so that can be very risky. For example, have you ever seen a smartphone that drained down to 1% and then held on for along time there? That's because it was wrong about the remaining battery life, and of course that type of error is convenient, but the opposite scenario is that the device will suddenly die even though it thought it had 5% remaining -- again, because it measured remaining life incorrectly. The closer to 0% the battery is, the harder it is to measure accurately because of how battery chemistry works.