Shouldnt of this flask saved my life?

Maybe i mis understood how these types of flasks worked, but with all information i could find i came to the idea that i shouldnt die as long as i hav charges?

http://imageshack.us/photo/my-images/402/14234.jpg/


Would love some light shown onto this..

It means it doesn't take time to refill the hitpoints, it doesn't automatically activate itself.

Thanks for that :)