I am looking to extend my battery life for my phone. what is the standard battery mah that comes with our phone? would anyone recommend this one? and i am not sure how this works, since they don't show a picture of how it works. can you plug in a battery, plus a phone with a battery? lastly, does the charging cord have to be of certain specs to charge a different battery? so if i have a 2000 mah, and i use a cord to charge that one, can i use the same one on a 3680 mah one?