Even if the clock/CMOS battery is bad, the memory checksum error sounds like a separate issue. Try swapping out the RAM in your system, or if you have more than one memory module, running only one at a time (booting up once with each) to see if the error goes away, and also create a Memtest86 boot disk (do a Google for memtest86) and test all your memory.
As you said in your opening post, PC Chips mainboards are cheap: both in price and in quality. With this in mind, their capacitors likely come from a pretty low bidder. Unless you have other equally cheap parts in your system, if the RAM tests pass the mainboard would be high on my suspect list of parts.
Intel Q9450 @3.2GHz, Gigabyte GA EP45-UD3P, 4 x 2GB G.Skill @4-4-4-12
Antec P160SW case (modded), Xigmatek 750w PSU
3x 500GB (RAID-5), , OptiArc 7200S, ASUS E818A3T
Creative X-Fi XtremeGamer, Hauppauge HVR-1800, Radeon 4890