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Solar cell watches like Citizen ECO-Drive, Seiko SOLAR etc

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--- Quote from: Koray on November 16, 2021, 07:39:28 pm ---Thanks for your reply. Here is the user manual for this watch. Please show me where it warns about complete discharge?

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Well, I can't find any promise for watch to be perpetuum mobile either. One is clear: "*Specifications are subject to change without prior notice." and " From fully charged to stop: Approx. 5 months (two-hand model)". That should ring (some) bells.

Btw, the watches use Lithium Titanium batteries, aka Lithium Titanate. These are characterised as having very high cycle life compared to other chemistries and very fast charge acceptance - handy for making use of occasional sunshine exposure. They do have lower energy density and cell voltage (2.4V) than other types.

I haven't found any specific data, but I suspect they are as susceptible to total discharge damage as any other Lithium cell. It's just not something you do to them, especially for very long periods.

The Panasonic part I've seen put in EcoDrive watches is a Manganese Titanium Lithium chemistry with a nominal cell voltage of 1.5V and charging voltage of 1.8V to 2V or so.


--- Quote from: Gyro on November 14, 2021, 10:43:03 am ---Yes, it is a rechargeable lithium cell, not a capacitor. If it has been left in the dark for 3 years then it will have discharged to zero volts (even when the battery has discharged to the point where the watch stops, it still has leakage current). No rechargeable Lithium cell, regardless of it's chemistry, will tolerate that. If she had stopped the watch before putting it away (as the manufacturers and jewellers do), it would have survived.
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This page says: " it only has a 10% a year self-discharge rate, and so is used in solar charged watches with expected life of 15+ years with shallow discharging."

So, would the battery circuitry really discharge it down to 0V and kill the cell. Seems unlikely, unless its a poor design, or bad cell no? I think OP needs to open it up and measure the actual voltage, see if it can be recharged.

Datasheet itself only goes down to 1uA/30 days:


My Citizen Eco-Drive watch is over 22 years old, and I cannot detect any deterioration of the storage cell. If it is lithium based chemistry indeed, it broke all the limits that the datasheets specify. Ain't I lucky that watch storage cells do not read datasheets ...

Cheers  Peter


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