How quickly do batteries lose their charge?

[emilysium]

I've heard before that you should have a plastic covering on your camera batteries when you're not using them, so that they don't drain.

I'm not sure whether this is a myth (i.e. using IS on a tripod harms your equipment), or whether there's some validity to that.

Any anecdotes or hard data, anyone?

[Mike R]

A cover protects the terminals from shorting out if they come in contact with metal. It's a safety issue and has noting to do with battery drain. Different battery technology will drain at different rates when not used. The environment also plays a factor in it. Try to stay away from Ni-Cd batteries, that technology is the worse.
As far as an anecdote: I had a batter short against a keyring in my pocket. I noticed it when the battery became so hot I got burned. It's a good thing it didn't explode in the pocket., That would hurt!

[emilysium]

Ah, that's good to know. I use NiMH batteries and just toss them around. Any issues with those?

Though, I was actually thinking of the BP511A batteries, and how the original Canon's came with plastic coverings that I have now lost all but one of. Those I'm also mean to, and just toss around.

I never paid attention to my batteries before. So from what I understand, if metal touches the + and - side of the battery at the same time, then it'll short circuit. What does the B and P stand for on it's underside?

[Mike R]

Not sure about the BP, I never paid much attention to what was written on them.

[JohnJ80]

All batteries discharge internally over time. Whether you have a cover on the contacts makes no difference unless a conductive material connects to the + and the - terminals at the same time. That is a short circuit and can rapidly drain the battery but, most importantly, is also a fire hazard. For safety's sake, you should protect at least one terminal to prevent this.

Standard NiMH batteries discharge about 1% per day just sitting on the shelf. The newer slow discharge ones (like Eneloops) will discharge about 20% a year. I don't know what the numbers are for Li-ion, but they are much better.

All batteries eventually will die from age.

J.

[r.morales]

Most batteries lose their charge faster as they get older .
You can check how long different batteries will hold a charge by plugging in a charger .
I have a power strip about 4 foot long with with 5 plugs . I have my e-loops charger in one , the portable hard drive in one and 3 canon chargers in others .
Once the batteries are charged up , turn off strip . Next day turn on and see how long before green charged lite comes on . Same thing after 3 days .
I have a sandisk memory card holder that holds 2 batteries for my XTI and clips on bag . I still keep covers on all batteries . I have a plastic case that holds 8 AA / AAA batteries for flash . It stays in camera bag .