[LG Optimus G Pro] uppon2:
This might not work for you as it did not work for me but it is the only way I have been able to pass the low battery message so it might work for some. I get a connection problem after step 3

Step 1.

Download tool and LG drivers (if you don't have them) from here and here and install them normally

Step 2.

Remove battery and note down your device model and serial number. Boot phone in to download mode by switching phone off or pulling battery if soft bricked, then hold down both of the volume keys and plug in the USB data cable

Step 3.

Run LG Mobile Tool and wait for the software to tell you it recognises the handset as either being the latest software or a new update is available. Unplug the handset but keep it in download mode then in LG Mobile Tools click on options then update recovery. It will now prompt you to enter your handset details, fill out the top 2 boxes and click ok. You will soon be prompted by a message asking you to plug your handset in, plug it in then press retry. Wait EXACTLY 5 seconds (count 1 Mississippi, 2 Mississippi, 3 Mississippi, 4 Mississippi, 5 Mississippi) then unplug the phone as quickly as possible! Very important, it might take a few tries to get it so just alter the speed at which you are saying Mississippi lol!. If you get the same error message about battery too low then you have failed and need to try it again. Once you have succeeded you can do either of the 2 things below:

3a. Plug phone back in immediately and wait for the file to download and flash (recommended) (I am currently trying this and will report back as soon as I can)

3b. If you are soft bricked and scared you have limited battery then don't plug it back in, pull your battery out and let the program run and it will do everything including download the required software for flashing. When the software is almost completely downloaded, boot back in to download mode and let the downloaded software flash to your phone. (might have an error at software installation this method. I couldn't get it to work I think due to the phone being disconnected for so long.)

Step 4.

MAKE SURE YOU DO A FACTORY RESET STRAIGHT AFTER THE SOFTWARE HAS INSTALLED

Step 5. (Optional)

Download the older version of FreeGee from here if you are still a bit unsure if the latest version will soft brick your handset again.

I have managed to use LG Flash Tools now, even after being affected. I would not advise trying this though, as it was an accident for me. I had the back cover off while flashing a custom rom with CWM. After the rom file was installed, I rebooted my phone from CWM. As the phone was rebooting (was on the rom boot animation) the battery fell out. After I put the battery back in the phone would load to the rom boot animation, but it would freeze on this screen and then reboot and do the same thing over and over (bootloop to animation) - I then tried to factory reset and flash the rom again, with the same thing happening again) - I then went in to restore my phone using a backup through CWM. After the restoration, then phone would still hang at boot animation and then bootloop. I retried restoring and flashing multiple roms and re root the phone with a saved zip file on my phone. None of this was working. I decided to try to use LG Flast Tools again, only this time it actually passed the low battery warning. The funny thing is, I have tried thousands of times even at 100% battery level and lower (when there was nothing wrong with my phone at all) and it has never worked. This time it did (even though I had 66% battery) and still works now, as I just tried it again.