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I have a Casio C-80 vintage calculator watch. All the functions are working but the time is ticking way too fast. I suspect the batteries in the watch is not the correct ones. Does anyone know the proper replacement battery model number? Thanks!
 

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From what I read apparently 381/391,LR1120 batteries are suitable. I think if the watch still misbehaves after battery replacement perhaps you might have a faulty module.
 

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Batteries are pretty standard. Lithium is different voltage to silver oxide or alkaline. Otherwise the size matters only as far as physically fitting into the watch.

It is far more likely that the quartz oscillator has degraded over time. A molecule or two gained or lost here or there is making it vibrate a little faster. If the module has a rate trimmer circuit, then it might be possible to improve the performance.
 

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It currently has two LR1120H batteries in it which requires a paper shim to fit properly. Maybe it does have a bad module. It was sitting in my drawer for 30 years so guess I can't expect much.
 

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I've uploaded a short video showing the clock speed but this forum won't allow me to post links. Please go to YouTube and search for "c-80 running wild".
 

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Did you reset the watch (+ to AC) after you installed the battery? Most Casio watches misbehave if you skip that step. Take the case back off and look for a spot marked AC(All Clear) and take a paper clip and touch the AC while touching the top(+ side) of the battery and see if this assists
 

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I've uploaded a short video showing the clock speed but this forum won't allow me to post links. Please go to YouTube and search for "c-80 running wild".
This is his video:

I hope journeyforce's advise helps. Reset is pretty standard step for these.

if nothing helps you can always try to find C-80 in very very bad condition but with properly working movement so you can buy it cheap and just swap movements.
 

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That doesn't look like a degraded oscillator. Reset must be the way to go.
 

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That is great.

Casio watches are funny. I have gotten vintage Casio watches that the seller(or person that gifted it to me) stated that they put a new battery in it and it still did not work. I put a new battery in and was able to duplicate the non working issue. I then AC reset it and it worked perfectly.
 
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