After upgrading to Mac OS X 10.5.8 on the MacBook Pro 15 in (early 2008), my wireless network speed plunges when on battery power, compared with adapter power. Ping to the nearest network router on AirPort Extreme should be ~1ms (and is when on adapter power) but increases to 300ms when the adapter is pulled.
Resetting the system power management unit (SMC) does NOT help.
#61: MacBook Pro network access slow on battery in 10.5.8
Solved!on August 08, 2009, 10:30 PM UTC — from 
yliu ( 3,543 views )
yliu ( 3,543 views )
Replace IO80211Family.kext with a previous version
- yliu on August 08, 2009, 11:10 PM UTC
If you're using Time Machine, this is simple enough. Pull a version of IO80211Family.kext (the AirPort driver) from before the system update.
If you're not, this involves grabbing the 10.5.7 combo updater and extracting the package (with Pacifist) for IO80211Family.kext. Once you get this file, remove the new copy and put your old one in its place in /System/Library/Extensions. Then, issue
to clear kernel extensions caches. Reboot and get back your AirPort speed even on battery power.
When replacing the broken kext, make sure that permissions are set properly on the new kext. On occasion, copying (via the Finder) will set owner, group, and their permissions for the .kext file to something unacceptable to the OS. For security reasons, kext files and their resources in /System/Library/Extensions need to be root:wheel owned. A Repair Permissions via Disk Utility is probably the best option, though you manually
If you're not, this involves grabbing the 10.5.7 combo updater and extracting the package (with Pacifist) for IO80211Family.kext. Once you get this file, remove the new copy and put your old one in its place in /System/Library/Extensions. Then, issue
kextcache -k /System/Library/Extensions/to clear kernel extensions caches. Reboot and get back your AirPort speed even on battery power.
When replacing the broken kext, make sure that permissions are set properly on the new kext. On occasion, copying (via the Finder) will set owner, group, and their permissions for the .kext file to something unacceptable to the OS. For security reasons, kext files and their resources in /System/Library/Extensions need to be root:wheel owned. A Repair Permissions via Disk Utility is probably the best option, though you manually
chown -R root:wheel /System/Library/Extensions/IO80211Family.kext as well.References used:
10.5.8 slow Airport when on battery
( http://discussions.apple.com/thread.jspa?threadID=2106968&start=105&tstart=0 ) - found by
yliu on August 08, 2009, 10:31 PM UTCMac OS X 10.5.7 Combo Update
( http://support.apple.com/downloads/Mac_OS_X_10_5_7_Combo_Update ) - found by
yliu on August 08, 2009, 10:33 PM UTCOS X kexts knowhow
( http://blog.skaelede.net/archives/2007/02/07/os-x-kexts-knowhow/comment-page-1/# ) - found by
yliu on August 08, 2009, 11:03 PM UTC
Think you've got a better solution? Help yliu out by posting your solution
OS X kexts knowhow
http://blog.skaelede.net/archives/2007/02/07/os-x-kexts-knowhow/comment-page-1/# - found by yliu on August 08, 2009, 11:03 PM UTC
clearing kernel caches after installing a new kernel extension
Mac OS X 10.5.7 Combo Update
http://support.apple.com/downloads/Mac_OS_X_10_5_7_Combo_Update - found by yliu on August 08, 2009, 10:33 PM UTC
The last working OS X version.
10.5.8 slow Airport when on battery
http://discussions.apple.com/thread.jspa?threadID=2106968&start=105&tstart=0 - found by yliu on August 08, 2009, 10:31 PM UTC
and of course, there are other people bitching about already