How much energy does a typical digital watch use?

[Trần Thành 23456]

is this at 1.55Volt LR41 battery and the current can come to microAmpe?

[Ghideon]

6 hours ago, Trần Thành 23456 said:

is this at 1.55Volt LR41 battery and the current can come to microAmpe?

Assuming that a LR41 battery lasts for 5 years in a digital wrist watch and initially contains 30 mAh then a quick calculation gives the average current 0,46 micro amperes.

[mistermack]

1 hour ago, Ghideon said:

Assuming that a LR41 battery lasts for 5 years in a digital wrist watch and initially contains 30 mAh then a quick calculation gives the average current 0,46 micro amperes.

I don't think it works quite as simply as that. Batteries will degrade over five years, even if you are not drawing a current. So some of the 30 mah will have been used, but a substantial amount will have just seeped away due to aging. 

[Ghideon]

3 hours ago, mistermack said:

I don't think it works quite as simply as that.

I agree, a detailed analysis requires more assumptions and/or information from OP. Let’s try to rephrase the answer: under the stated assumptions, constant power usage, and ideal and lossless conditions the current will be below 1 micro ampere.

 

[StringJunky]

58 minutes ago, Ghideon said:

I agree, a detailed analysis requires more assumptions and/or information from OP. Let’s try to rephrase the answer: under the stated assumptions, constant power usage, and ideal and lossless conditions the current will be below 1 micro ampere.

 

There's always some parasitic discharge somewhere in a cell, isn't there?

[Ghideon]

1 hour ago, StringJunky said:

There's always some parasitic discharge somewhere in a cell, isn't there?

As far as I know that is generally true, I'm unaware of any battery chemistry that allows for unlimited storage. Self-discharge depends on storage environment, chemistry, brand, temperature (and probably others I have missed). I intentionally neglected all this in my ball-park calculation. Another thing I neglected is that a wrist watch may have functions that temporary draws additional power; backlight, alarm etc. Maybe OP returns with follow-up questions or additional information to take into account...

[mistermack]

You could also look at it from another view point, and work out how much energy was used in making the battery, and that gives a more real total of energy used.