Battery used.

Yes, the photo show this is what happen when you using few times of battery and then leave it don't use for long time. 

I not sure is this mouse still can works or not, because i seldom use this mouse. The mouse looks like has a very cold frozen ice but its not, it is a liquid form from the battery die when not using.

Let me explain about the battery usage, whatever you buy a rechargeable or Non-rechargeable battery is still the same lifetime care process either one.

If you not using, please fully discharge the battery until empty no more power inside and then you are save to keep it anytime. How to discharge? Well, used it until no power or used handheld torchlight turn it ON and leave it until drain out battery power. But, battery has a size AA, AAA or what else, just put in the torchlight that can fit actual size of battery. 

For Non-rechargeable battery, please used it until drain out battery power then only throw away. DO NOT leave it or keep it whatever it still 10% or 5% power inside. This may cause the problem that i had before. One way or another, inside the battery still have or some power inside it may cause it definitely.

If you think this is nothing, then keep doing what you think is correct way. This may damage air environment, will reduce some radiation which is very harmful to human.

If you still want used it sometimes, then you only charge it back and of course need take some time to charge it full.

This is how it works, everything has a lifetime need to be smart to using every single thing.