The other day I turned on my computer (after it had been off for about a week) and it would not boot up--I received a "critical low battery" error. The thing is, there was no battery in the machine. I popped in a long-expired battery to see what would happen and the computer would not even turn on. I have ruled out the A/C adapter--I have another laptop of the same model which boots up just fine with either adapter, but this one will not boot with either. I finally got the machine to boot up by popping in the battery at a strategic moment just before the error appears. It works fine as long as I leave it running, cbatterie.com, but Windows thinks that it is running from the battery ("Current Power Source: Batteries - Total Battery Power Remaining: Unknown") and the computer dies instantly if I remove the battery. I have tried uninstalling and reinstalling the battery in Device Manager to no avail. Is there anything else I can do, or do I need to make the backup laptop my primary?