I recently came to the same fate, Recently had my battery replaced by Dell which was wonderful n the mess up part is that I cannot get it charged on my L attitude E6420.
My flashing problem started when I had a power failure in my area while i had my note book on charge. I cant do anything without having to keep my notebook on charge. i doesnt start up without it being plugged in now n it doesnt even charge my new replacement battery.
Any suggestions?