Here is a little perl / applescript I put together that monitors the status of my battery level. When the battery gets to a low enough threshold, an alert prompt is displayed so I know that it's time to start thinking about plugging the computer back in. This idea started after reading this hint.

You will see my comments if you scroll down (look for kb5ql).

To proceed, you will need to perform the following steps:

1. download and install the battery_check_alert script
2. change the permissions on the downloaded file  read more »