As for the CMOS battery if the system is just rebooted the the date should stay correct, during shutdown then start up and loss of hibernation is when you would loose the date.
Windows Defender is not really an anti virus/malware program and has not been update is a couple of years.
I would recommend you download, install and run Microsoft Security Essentials
, make sure you run a Full scan.
How much ram does your laptop have?