How Often Should I Charge My Streamlight Stinger LED?

My employer has issued me a Streamlight Stinger LED. There are gang chargers that we are supposed to use to charge our lights. I am just wondering how often I need to charge the light. Today, for example, I used it a couple of minutes, but I left it at work and I don't return to work until Monday at 7 AM. Do I need to charge it right away when I get there and, if so, how much? Unlike my Inova T4 and Pelican 7060 with lithium ion batteries, I really don't know when the Streamlight Stinger is fully charged. I guess they are designed to be left on the charger all of the time, but in my situation that really isn't an option. Should I get a single charger, bring it home, and bring it in fully charged and ready to use or can I get by with the small amount of usage by just charging it for an hour or two?

It's a Ni-Cad battery so unfortunately it will lose it's charge after an extended period...but we are talking at least several weeks without use if the battery is newer, but it shouldn't drop too noticeably just over a few days. I had mine off of the charger for a month once and while it ran fine for a few minutes the battery didn't hold out long after that...only ran for about ten minutes before dying out. With an LED you'll likely get better low end run-times but even still you will need to be able to charge it to full capacity at some point which will require more than a couple of hours....so yes, I would suggest that if you cannot leave it at work over your weekends that you pick up a charger for it...or expect the battery to die just about the time you need it.