PowerShell script to help to keep laptop battery level in the specified range. Not automatically! You need to plug-in or unplug cable when you hear alert sound :) See: http://www.mmdemirbas.com/2013/03/monitor-remaining-battery-level-using.html

battery.ps1

#########################################################################
#                                                                       #
#    Script to check battery state periodically and alert if it is      #
#    going to outside of the desired range (%40-%80) by default.        #
#                                                                       #
#    Usage:                                                             #
#                                                                       #
#           # To alert if x<=40 or x>=80, and check each 15 sec         #
#                                                                       #
#           .\battery.ps1 40 80 15                                      #
#                                                                       #
#                                                                       #
#    Author: Muhammed Demirbas, mmdemirbas at gmail dot com             #
#                                                                       #
#    Date  : 2013-03-26                                                 #
#                                                                       #
#########################################################################

# Default values for parameters
param($lowerLimit=40, $upperLimit=80, $interval=15)

# Function to return first non-null value among its arguments
Function IfNull($a,$b) { if($a){$a} else {$b} }

while($true)
{
    $obj                 = (Get-WmiObject -Class Win32_Battery -ea 0)
	$remainingMinutes    =  IfNull $obj.EstimatedRuntime          "N/A"
	$remainingPercentage =  IfNull $obj.EstimatedChargeRemaining  "N/A"
	$statusString        =  switch (IfNull $obj.BatteryStatus 0)
							{
								 0 { $pluggedin=0 ; "N/A"                   }
								 1 { $pluggedin=0 ; "Discharging"           }
								 2 { $pluggedin=1 ; "Plugged in to AC"      }
								 3 { $pluggedin=0 ; "Fully Charged"         }
								 4 { $pluggedin=0 ; "Low"                   }
								 5 { $pluggedin=0 ; "Critical"              }
								 6 { $pluggedin=1 ; "Charging"              }
								 7 { $pluggedin=1 ; "Charging and High"     }
								 8 { $pluggedin=1 ; "Charging and Low"      }
								 9 { $pluggedin=1 ; "Charging and Critical" }
								10 { $pluggedin=0 ; "Unknown State"         }
								11 { $pluggedin=0 ; "Partially Charged"     }
							}
	
	if ($remainingMinutes -ge 1000) { $remainingMinutes = "N/A" }
	
	if     ( !$pluggedin -and $remainingPercentage -le $lowerLimit ) { $alert = "Connect AC!"    }
	elseif (  $pluggedin -and $remainingPercentage -ge $upperLimit ) { $alert = "Disconnect AC!" }
	else 
	{
		$alert    = $null
	}

    $forecolor = if($alert){ [ConsoleColor]::White     } else { [ConsoleColor]::Gray      }
    $backcolor = if($alert){ [ConsoleColor]::DarkRed   } else { [ConsoleColor]::DarkGreen }

    $log       = "[$(Get-Date)] Remaining: $remainingPercentage% ~= $remainingMinutes minutes. $statusString. $alert"

    Write-Host -ForegroundColor $forecolor -BackgroundColor $backcolor $log
	
    if ($alert)
	{
		[System.Media.SystemSounds]::Hand.Play()    # Play sound
	}
	
	Start-Sleep -Seconds $interval
}