Like any battery it all depends on how much you use it. If you use it heavily then I suggest that you let it cool down between uses, this will help extend the life of the battery.
A pellet gun is capable of serious injury or death depending on where the victim is struck. The shooter could be charged with battery or a greater crime. Never point a pellet or BB gun at anyone.......
it lasts up to 3 hours
2-4 hours depending on your airsoft gun
It depends on the model and the caliber of the Pellet gun.
I assume you are asking about air guns, if so then it would be helpful if you stated the model. Most air guns can accept all weights of pellet grains as long as the pellet is the correct caliber. In other words you can not use a .22 pellet in a .177 caliber pellet gun but you can use different weight pellets as long as they are .177 for that gun.
I think you mean pellet gun. That is a gun that fires a small lead pellet but does not use gun powder. It uses compressed air or compressed gasses to push the pellet.
A pellet gun is not adequate for protection, and will get you arrested.
It all depends on the model and who made the pellet gun. I suggest that you re-post the queston with the model and make of the pellet gun to get an answer.
Any pellet gun should be handled like a real firearm. Yes you can be killed with a pellet gun under the right circumstances.
No. Even if it would fit in the chamber, there is no firing pin on a pellet gun.
Nope. Pellet guns are fairly safe to use.
No. A pellet gun would use compressed air.