I would agree the battery is suspect. BIOS resets can occur for unexplainable reasons I've found, though there is always a reason of course, whether we find it or not.
Here is the reason I didn't see this thread until now...... maybe it could be relevant.
The last day or so I've been busy trying to upgrade a system for a friend of mine with a new mobo and cpu.
I met a plethora of obstacles and I thought it was all sorted out, when finally, after about 20 hours working on the darn thing and after I had it all tidied up and case modded, the thing refused to find the boot drive consistently and showed various errors. This practically had me in tears for a while as I had just installed a complex OS I did not wish to lose after so much work.
My experience has shown that IDE and other I/O controllers can be finicky at times and they are sometimes not very forgiving when it comes to the way drives are connected.
After another hour of fiddling with different configurations, it turned out that the Primary IDE channel needed both it's master HDD and slaved DVDROM drive set to CABLE SELECT by jumper and not MASTER and SLAVE, even though the cable positions were correct for both devices and they were set to MASTER and SLAVE respectively and correctly.
CABLE SELECT was the only configuration that ended this debacle finally and thankfully. This was the first VIA chipset I've messed with for a long time and I'm not too impressed or familiar with it at all. The Board is an Asus K8V-VM and it has no CPU or FSB configuration available at all