battery operation & time date keeping

I found all the 5V connection joints cannot be switched off ,except I pull away the USB power jack. The fan will run forever using the power on board. While the date and time will lose if now power. Even the D&T can be automatically update from internet, I prefer the timer running off line. I will try some switch circuit to solve the problem. Does anyone know how to do with software or easy connection on board ? May be a battery connected to some connector or joint?
I know a battery can be installed in mother board to keep the CMOS, but I cannot find any connector for the backup battery on LP.