I recently bought (1 month ago I think) this wireless usb mouse. Today it stopped working and the led doesn't light up anymore. I measured with the multimeter the two 1.5V batteries inside and found:
1st battery: 1.430 V
2nd battery: 0.19 V

Is it normal that one battery is fully charged while the other is fully discharged?
If the answer is yes, which one sis charged first?
And why?
How come they don't discharge together a little at a time?

It is a curiosity.

 

Normally, yes, I would expect both batteries to discharge approximately equally.
Perhaps one of them was bad from the beginning.

 

It's not common, but I've encountered it often enough. I've even seen a dry cell holding a slight reverse charge for a while. As suggested, it's probably a manufacturing error resulting in a bad cell.

 

Buy two fresh batteries in a single pack and start again.

Personally I dislike wireless mice because I would frequently drop them on the floor. Something that did not happen with mice with "tails".

 

Is it normal that one battery is fully charged while the other is fully discharged?
If the answer is yes, which one sis charged first?
And why?
How come they don't discharge together a little at a time?

With unmatched cells, the weak one will discharge faster. Were these batteries initially new and from the same package?

Even with matched rechargeables, some cells will eventually become weaker than others. This is a primary failure mode in battery packs. If the stronger cells are allowed to drive one or more weak cells into a reverse voltage state, that cell is probably irreparably damaged.

 

I think that we may all be assuming that the two cells are in series.

I had a wireless mouse a while ago that used one AA cell for some functions, and a second AA cell for other functions.

Sure enough one cell would go flat long before the other. Always the same one.

Mouse is long gone, so I cannot investigate further.

 

Sure enough one cell would go flat long before the other. Always the same one.

Interesting. I must remember to check the cell voltages in my mouse next time I need to charge the cells.

 

I have a wireless mouse that uses only 1 AA cell.
It must have some sort of boost circuit for circuitry power, since the battery can go down to below a volt before the mouse quits.
And that one battery lasts many months, even with daily usage for most of the day.