[OM] Lithium batteries

[Clyde Soles]

This is what the FAQ says:

Also, a lithium cell the size of two SR44's will *not* work
        properly in those cameras that take SR44's.  It will power the
        camera OK for a while, but its voltage will quickly drop below the
        minimum necessary for proper operation.

My question is: how long is a "while?" Using OM4t's, can I get 4 OK 
weeks of daily shooting? 2 weeks? 2 days?  I'm interested in the cold 
weather performance of lithium versus silver or alkaline.