Congratulations on getting your Reader going again.
I have 2 505s, that are 2 years old, and they have never been turned off. I use a wall charger and make it a point to charge them every 2 weeks or as soon as it gets close to 1/4 battery.
The suggestion above, by scarter, about getting a cheap PSP charger from Target or even a Game Stop store is a good one. You don't have to worry about leaving your computer on and it will usually take less than 4 hours to completely charge up. Making sure to keep it charged will probably help with not having to deal with a problem like this again.
Click on my signature for more information on MR (MobileRead) about the Sony Reader.