Why do my batteries suddenly discharge?

I am confused about what "self-discharge" actually means in batteries?

• So I was looking at lithium-ion batteries on Wikipedia (http://en.wikipedia.org/wiki/Lithium-ion_battery) and it mentions different self-discharge rates at different temperatures (per month). Lithium-ion batteries are rechargeable, so when they mention the % of self-discharge per month, are they talking about PERMANENT self-discharge (batteries rechargeable maximum capacity is lowered) or just temporary self-discharge (not permanent)? Also, if I put a lithium-ion battery in the freezer (inside a plastic bag or something), would it still retain most of its maximum capacity after a few years?

• Answer:

  Self discharge is not a permanent loss of battery capacity. If you charge a battery up and then just leave it sitting there, over time the charge is slowly lost. The rate at which the charge you have put into the battery wastes away is the self discharge rate. For example, if a battery had a discharge rate of 10% per month, and you charged it up and then just put it in the cupboard and left it there, when you came back a month later it would be 90% full. However if you put it back on charge again you could replace that 10% and bring it back up to full. Another way of looking at it is to imagine the battery as being a bucket with a small hole in the bottom. You fill the bucket up with water. leave it, slowly the water trickles out the hole but you can always fill the bucket up again.