No ethernet connection when power cable unplugged.

I work on a laptop. When my laptop is on AC, and I plug an ethernet cable in, the ethernet connection works automatically and connects immedietly.

However, when I work on battery and plug in the ethernet cable, nothing happens and I can't get connection.

Extra info:
apport info is added

In attachment: (data.zip)
cat /proc/version_signature > version.log
sudo lspci -vnvn > lspci-vnvn.log

This is a ubunut 13.04 release; it was upgraded from a (clean) 12.10

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: linux-image-3.8.0-19-generic 3.8.0-19.29
ProcVersionSignature: Ubuntu 3.8.0-19.29-generic 3.8.8
Uname: Linux 3.8.0-19-generic i686
ApportVersion: 2.9.2-0ubuntu8
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: pieter 1526 F.... pulseaudio
 /dev/snd/controlC0: pieter 1526 F.... pulseaudio
Date: Mon May 6 14:30:50 2013
HibernationDevice: RESUME=UUID=c5fe02d9-bcc4-4a09-bc0b-d029b705fa2e
InstallationDate: Installed on 2013-04-29 (6 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release i386 (20130424)
Lsusb:
 Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
 Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 002 Device 003: ID 0a5c:5800 Broadcom Corp. BCM5880 Secure Applications Processor
MachineType: Dell Inc. Latitude E6520
MarkForUpload: True
ProcFB:
 0 inteldrmfb
 1 nouveaufb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.8.0-19-generic root=/dev/mapper/ubuntu-root ro persistent quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.8.0-19-generic N/A
 linux-backports-modules-3.8.0-19-generic N/A
 linux-firmware 1.106
RfKill:
 0: phy0: Wireless LAN
  Soft blocked: no
  Hard blocked: yes
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/11/2011
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A06
dmi.board.asset.tag: pietervdvn
dmi.board.name: 0J4TFW
dmi.board.vendor: Dell Inc.
dmi.board.version: A01
dmi.chassis.asset.tag: pietervdvn
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA06:bd07/11/2011:svnDellInc.:pnLatitudeE6520:pvr01:rvnDellInc.:rn0J4TFW:rvrA01:cvnDellInc.:ct9:cvr:
dmi.product.name: Latitude E6520
dmi.product.version: 01
dmi.sys.vendor: Dell Inc.