Originally Posted by sidebrnz
FYI, on modern Mobos, the CMOS is designed to make the clock run slow if the battery's weak, giving you a warning that it needs replacement. If the clock's gaining time, or the change is random, it's very unlikely that the battery is the issue.
Not true. The CMOS clocks run off a crystal oscillator (similar to a watch) that either runs at the spec frequency or doesn't run at all. The gating of the counters is all deterministic. There is no "slow down" feature in the design.
When the voltage is low the oscillator may not operate or the CMOS gates will fail to clock and/or fail to keep it's settings. It can clock incorrectly on a gate-by-gate where this is more likely to impact the higher frequency but lower drive current gates (internal higher frequency counters). So in some cases a low voltage condition can result in missed clock counts, but this is not a design feature but an artifact of the CMOS design and is not a reliable symptom.
My experience is the dead-battery CMOS clock will most often lose the value of current time when powered off and resume from a 'garbage' or 'semi-random' time when power is reapplied. Of course when the system is powered up it operates normally, but from an unacceptable starting value.
So either random time values or random amounts of lost time, or time lost equal to time since last shutdown represent a possible CMOS clock battery failure.
OTOH if the OPs clock is always off by LOCALTIME-UMT hours - that's a different story. IF the OP sets the time, then as the system runs he loses time ... that's yet a different story. Without more info all suggestions represent a 'shotgun' approach and not a diagnostic cure to the problem.