Appreciate the reply Steve nevertheless. If you, with your far superior knowledge of clocks is stumped, then I think I have no hope of ever finding the answer. As I type this, the clock is still keeping time for two hours after having to reset the time (it was 18 minutes off). Which reminds it, it tends to lose more time during different times of the day. So perhaps, there is a worn cog or some debris that is interfering. I might try oiling it if I'm at the point of throwing it out. Perhaps the higher voltage of new batteries causes the cog to skip and go backwards... Now I'm just making stuff up! I agree they don't make clock movements like they use to. I have several other cheap and cheerful quartz clocks (shed, garage, laundry) that have no problem keeping time - perhaps the Japanese quartz movement is still the key. I see there are some clocks with German quartz movements on the market. I hope precision German engineering applies to their clocks as well. If anyone can share any reliability or accuracy data, I'd be interested to hear from you. Thanks again Steve. I hope haven't polluted your forum too much with an off topic post.

Thanks for the insights Steve. Your random guesses are plausible, however I have tried all types of batteries chemistries (Alkaline, Carbon Zinc, NiMh) from different brands (cheap and premium) and they all exhibit this weird behaviour. I probably tried 10 different types, so I don't think it's the battery. Could it have something to do with the internal resistance of the battery as it ages? When it ages, it increases but also reduces the current available. But my electrical engineering knowledge is too rusty to deduce what impact that might have to a DC motor and associated circuitry. I already had the original quartz movement replaced 3 years ago under warranty - my second in 6 years - so suspect the movement itself is garbage. Something I didn't expect from Seiko to be honest. I'm less optimistic than you in finding a quartz movement that will last 10-20 years! I'm currently looking for a new wall clock, but it's hard to find one with a quality movement. I don't know if I can justify purchasing a $600 clock again only for its movement to fail in a few years time. I might have to give your 3D clocks a go when 3D printing becomes more readily available where I live. What kind of accuracy do your clocks have?