I received my T4210 today, along with the modular bay battery and 3M screen protecters. As soon as I unpacked it, I stuck in the modular battery, plugged in the AC adapter, and left it for about 5 hours until all the charging indicators were off and the batteries were cool. I then unplugged the AC, booted it up for the first time, and ran it until it died. For my first full discharge (from fully charged to auto-shutoff due to low battery), with both batteries installed, I got 7 hours and 5 minutes. Specs: 1.83GHz Core Duo 512Mb 667MHz DDR2 (will be upgrading soon) 80gig 5400rpm HDD Intel Wireless/Bluetooth Indoor-only screen During this time, the screen was set to the 3rd (out of 8) level, though I found indoor viewing of the screen at the lowest possible setting to be quite acceptable. I was using the system for the entire 7 hours; NO idle or standby time. I had the screen set to shut off after 3 minutes of inactivity, and this only happened 3 or 4 times (beer, bathroom, lol), with the screen going off for only a minute or so. In addition to continuously playing with the system in general (internet browsing, playing around in OneNote, etc.), I did the following during these 7 hours: - Installed and Uninstalled several programs (Symantec crap OUT; McAfee, photoshop, acrobat pro, firefox, partition magic, Acronis True Image, Nero Ultra, MSN messenger,Daemon Tools, video codecs, etc, IN) About half the installations were performed via DVD, half off of networked harddrive images. - Partitioned the harddrive. - Created a backup image of the OS/standard programs partition - Burned said backup image onto a DVD using the modular DVD drive (swapped the bay battery for the DVDRW drive for this operation and a couple of installations, then swapped back to the modular battery) - Used wireless network connection for 1 hour (browsing internet, testing the speed, transferring some files from networked desktop). After this hour, wired network was used, and the wireless on/off switch was turned OFF. - Shut-down and restarted many times (installations, partitioning, etc.), but never left it off for even a few seconds. - Watched maybe 10 minutes of video, listened to 5 minutes of music, and recorded a few 30 second sound clips to test the screen/speakers/mic. Every minute of spare time in between these things was packed with scribbling, transferring of music/vids etc. over network, browsing online, some editing in photoshop, a little IM'ing... I even did the tablet PC tours and tutorials, and tried the MS Tablet Experience pack or whatever it's called. I'm going to be quite busy in the next week or so, but I hope to test the life of just the main battery soon; but for now, I'm relatively satisfied with 7 hours.