This came across the Ga FLL yahoo group adn I thought it was important for everyone to realize:
The other day my team had taken one of their NXT bricks with them to a meeting. When we got home, the battery was completely discharged. After recharging it, my daughter discovered that the "Sleep" setting was at 60 minutes. The brick had accidentally turned on during transport and since the sleep setting was so long, it ran the battery down. We discovered that the 60 minute setting is the default for both the 1.26 and 1.31 firmware update. That is WAY too long!
If you have updated your firmware, you should check the sleep setting and change it is a more reasonable time (perhaps in the 2-5 minute time frame). This way you won't accidentally run down your battery. I'd hate for someone to discover their battery was dead when they arrived at a competition.
To access the sleep setting on the NXT brick, go to:
and then change the time with the arrow buttons