Code/tp-bat-balance

#!/usr/bin/perl
# Keep two ThinkPad batteries (system battery and UltraBay) at similar charge levels
# during discharge by switching back and forth. This reduces wear on the UltraBay
# battery, compared to the hardware's default strategy of fully draining the UltraBay
# battery before switching to the system battery.
# WARNING: This script is experimental and uses undocumented hardware features.
# WARNING: If this script crashes, your battery may be forced to keep draining until empty.
# Distributed under the terms of the GNU General Public License v2 or later.

use strict;
use warnings;
use File::Slurp;

my $thresh = 3; # difference between battery charge levels that justifies switching (hysteresis)

my $default_discharge = 0; # the battery that's discharged as first priority by the BIOS
my $smapi_dir = '/sys/devices/platform/smapi';

my $ac_connected;
my @bat_installed;
my @bat_remaining;
my @bat_state;
my @bat_power_avg;
my @bat_force_discharge;

$SIG{'INT'} = $SIG{'QUIT'} = $SIG{'TERM'} = sub { die("# Killed by SIG$_[0]\n"); };

sub read_chomp_file {
  my ($filename) = @_;
  my ($x) = read_file($filename) or die "Cannot read $filename\n";
  chomp($x);
  return $x;
}

# Read battery status from tp_smapi sysfs interface
sub read_status {
  $ac_connected = read_chomp_file("$smapi_dir/ac_connected");
  for my $b (0..1) {
    $bat_installed[$b] = read_chomp_file("$smapi_dir/BAT$b/installed");
    $bat_force_discharge[$b] = read_chomp_file("$smapi_dir/BAT$b/force_discharge");
    if ($bat_installed[$b]) {
      $bat_remaining[$b] = read_chomp_file("$smapi_dir/BAT$b/remaining_percent");
      $bat_state[$b] = read_chomp_file("$smapi_dir/BAT$b/state");
      $bat_power_avg[$b] = read_chomp_file("$smapi_dir/BAT$b/power_avg") / 1000.0;
    }
    else { $bat_state[$b] = 'none'; }  #This var needs to always have a value for print_bat to not break. This covers the case of starting the program without a battery in the bay/slot.
  }
}

# Print status to stdout (ASCII graphics)
sub print_status {
  print "   ";
  sub print_bat {
    my ($b) = @_;
    my ($ll,$lr,$rl,$rr) = $b ? ('-','>','<','-') : ('<','-','-','>');
    my $icon = sprintf("[%3s]", $bat_installed[$b] ? $bat_remaining[$b]."%" : "");
    my $arrow;
    my $state = $bat_state[$b];
    if ($state eq 'charging') {
      $arrow = sprintf("$ll--%4.1f--$lr", $bat_power_avg[$b]);
    } elsif ($state eq 'discharging') {
      $arrow = sprintf("$rl--%4.1f--$rr", -$bat_power_avg[$b]);
    } elsif ($state eq 'idle' || $state eq 'none') {  #Added none to cover case with no battery in slot when program was started.
      $arrow = "          ";
    } else {
      die "Unknown state $state for battery $b";
    }
    print($b ? "$arrow$icon" : "$icon$arrow");
  }
  print_bat(0);
  print($ac_connected ? ' {AC} ' : ' {  } ');
  print_bat(1);
  print("\n");
}

# Choose which battery to discharge
sub choose_discharge {
  sub set_force_discharge {
    my ($b,$on) = @_;
    return if $b!=$default_discharge; # the non-default battery will be discharged only when necessary anyway
    return if $bat_force_discharge[$b]==$on;
    write_file("$smapi_dir/BAT$b/force_discharge", ($on?'1':'0')) or die ("Cannot write to $smapi_dir/BAT$b/force_discharge: $!\n");
    print("# setting force_discharge on battery $b to $on\n");
    $bat_force_discharge[$b] = $on;
  }

  if ($ac_connected || !$bat_installed[0] || !$bat_installed[1]) {
    for $b (0..1) {
      set_force_discharge($b,0);
    }
  } else {
    if ($bat_remaining[0] > $bat_remaining[1] + $thresh) {
      set_force_discharge(0,1);
      set_force_discharge(1,0);
    } elsif ($bat_remaining[1] > $bat_remaining[0] + $thresh) {
      set_force_discharge(0,0);
      set_force_discharge(1,1);
    }
  }
}

while (1) {
  read_status;
  print_status;
  choose_discharge;
  sleep(5);
}

END {
  print("# Cleanup\n");
  write_file("$smapi_dir/BAT0/force_discharge", ('0'));
  write_file("$smapi_dir/BAT1/force_discharge", ('0'));
}