The comparison of best external batteries

Nowdays power bank--external battery is very popular and its market demand is becoming bigger and bigger.Many electronic device users find that it really useful in our daily life.And many people research it and pay attention to it.
I have researched this for a period time and find several promising external battery brand.The following is the comparison about them.I take samples that have the similar capacity to compare them.

From the above sheet,we can get some useful information.
1.On the condition of same capacity,RAVPower has lowest price,Anker is the second,then Powergen and NewTrent is the third.
2.The four brand external battery all can be compatible with mobile phone,but Anker and RAVPower can charger for MP3/4/5.Except for Newtrent,the other external battery are suitable for PSP,but Powergen cannot compatible with PSP vista.RAVPower also can charger for E-books and Anker can support for Nook Color.
3.The ouput voltage of NewTrent is a little lower than the other three.Higher ouput voltage can reduce the charger time.
4.Package:Newtrent is very simple,the other three are complete and RAVPower can provide a free bonus flannel bag for users.It's a sweet action for users.