It can be very difficult to place accurate probabilities on events that occur infrequently. Consequently, risks to equipment or personnel are hard to determine. My rule of thumb is if the probablility of something bad is greater than zero, I try to avoid it -- especially if I can do so at low cost..
The is something fundamentally unsound about raising an issue on a "forum," getting a reply of the type "I've never had a problem," and taking it as the Revealed Word.
All you have to do is to search "Google" using key words such as "NiCad battery leak" or using "NiMh" or "lithium" or "alkaline" or whatever, instead of NiCad. You will get a good many hits from folks who opened up some piece of equipment and found gunk all over the battery chamber and/or the circuit boards, etc. Are these people hallucinating? Extremes of heat, or cold, or over-charging, or who-knows-what can raise the likelihood that something will go wrong. What is the chance? I don't know. But storing things with their batteries inside suggests that you know. Do you? You're the one who has to make the decision.
I realize that removing/replacing batteries in some equipment is not easy. I also know that many folks put some device away, fully intending to unpack it in just a short period. Sometimes they don't get back to it until long after they intended to.
Many batteries, especially rechargeable ones, lose their charge just sitting there. If you have a product that can be adversely affected by trying to run it on low charge, this could jump up and bite you in the ***.
I always charge my batteries outside of the device that uses them.
Batteries are very commonplace in our society; so much so that very often scant attention is paid to them. That can be risky: If you want to have an "exciting" afternoon, just drop a battery (say a little AAA alkaline) in a pocket full of keys and loose change. But don't take my word for any of this. That's why the Great Spirit gave us Google.
