Howdy!
Back again after a divorce.
Just had to order the st90 from Wayne!!
After reading the threads about it i came to the conclusion that i don´t know much about batteries……
What´s an IMR battery?
What different protections are there? (i know of thermal protection)
Could i use protected batteries in the st90?
Good to be back!
Glad to have you back, Sgtpev! Welcome to the wonderfully free world of post divorce. Hope you didn't get raked over the coals. It's all worth it in the long run. 
for some answers see the flashlightwiki about rechargables.
Yep, both flashlight wiki and the link about batteries in my sig have a lot of information.
What´s an IMR battery?
A battery that can supply extremely large amounts of current due to a different internal chemistry.
What different protections are there? (i know of thermal protection)
Most protection circuits protect the battery from over charging (at 4.3ish volts they cut off charging), over discharge (at around 2.5 volts they stop the battery from dishcarging anymore) and over current (prevents a short).
Could i use protected batteries in the st90?
Yes.
Much obliged!
Will read up on batteries. Then im all set for the st90. 