Is it bad to keep my spare battery plugged in?

That is...plugged into the wall charger even though the light is green?
Any effect on battery life if this is done?

kuma1212 wrote in post #3873908
That is...plugged into the wall charger even though the light is green?
Any effect on battery life if this is done?

I wouldn't. Those rechargeable lithiums don't lose juice that fast.

Once its charged its best to remove them from the power and let them sit till you use them again...

It is best to leave these camera batteries in a discharged state and charge before use. Don't top them off after use and recharge them every 30 days or so like NiCd or NiMH cells. Even the info that comes with the Sterlingteck battery packs states not to store them in a charged state but deplete them first. Every time you put these batteries in a charger, it is one cycle and they have a limited amount of cycles--somewhere between 200 and 300 charges.

I keep my grip switch OFF unless I am going to use portrait mode a lot.

I normally use one battery in my grip at a time, unless I am going light (sans pack) then I will stick two batteries in the grip of the same or nearly the same capacity. It is not good to mix cells or packs of different capacities as they are drawn down together, and the one with more capacity will drain itself trying to get the other pack up to equal capacity. That's why I think it best to only use one pack at a time. You know when it is dead and needs to be recharged, and you know when you have a full pack in there. One battery pack is good for about 1,000 shots without using on-board flash.

It's not good to let Li Ion cells go flat. It's better to keep them with some charge in them; unlike NiMH or NiCd cells they break down when drained.