So recently, i've noticed my phone has been charging a lot slower in certain situations. If i charge from a mains, using an apple ipad plug, everything is fine. however ,if i charge at work using another plug, or i use my powerpacks, it charges at about a quarter of the speed. we are talking it takes about eight hours to get from 20% to 80% while the phone is off. but if i charge it at home the phone is done in little under two hours from flat. this is bothering me a lot because in little over a month i will be traveling for a month backpacking and 99% of my charge will need to come from the powerpacks i'm taking. any help with this would be greatly appreciated thanks!