I'm looking for a portable phone charger for my Samsung Galaxy S3. I want one that is fast and gives lots of charges. I did buy one at Walmart.It's a Pocketjuice and its 20,000 mAh and another number is 4.2. ( I don't know what the letters and numbers mean) I like it as its fast but its so big. Can someone explain to me what the numbers mean and what I should look for ? ( a friend has this charger and she says her phone gets hot !) Thanks for your help!