This is correct, while it is not likely that your unusually long boot time is due to a CMOS battery, it would still be a good idea to change it.
Most CMOS batteries will last for about 3 years or more, while another batteries will fail in 3 months.
You battery is located some where on your motherboard, and is most likely a CR2032, found in most any store, even Walgreens, and CVS stores for about $3.00. They are very common, and used in car dongles, fan controllers, and numerous other devices.
Your slow boot times, may be due to a load of executables opening that you're not aware of. It can also be due to a ton of fractured registry entries, and a numerous other issues.
If I were you, I wouldn't bother going crazy trying to find the problem/problems, I'd just format the drive, and reload a nice clean install of the OS which will cure any issues relating to the OS.