fanuc om help

IN hurry late other night, had batteries for memory backup sitting at machine for a couple of weeks
Decided to take care of before I wrap up and didn't pay close attention to battery install
tried to turn machine on a couple days later and nothing except tiny faint random letters on screen
immediately checked batteries and notice install was wrong
Checked normal install voltage (+4.5) checked voltage with my wrong install(-1.5)
Surely not Idiot to do this
Is there a diode to protect boards or did I really screw up
Machine is a makino rmc 55

Memory data is gone for sure. Hard to say if you messed up anything else. How does the display look if you have the batteries out completely? If it is Also, Is this a A. B, C. or D? Not sure if that will matter.