[TenTec] What's the keep alive battery do?

[jreed]

Hello, My Orion receiver is now having a problem
in that the display just comes up white and nothing 
after that...  If I hold the Main RX/TX button 
down while powering up, all goes well except that 
I then have to reset all the settings like power level 
mike gain, s-tone, etc etc....  Does this indicate that I 
need to change that battery and if so, how do I do that?

Jim Reed