Is it true that you have to use the charger which comes with your phone? Would it be bad to use my old Thunderbolt charger on my Razr? Does it even matter? Even if the voltage differs between each charger, they are both pretty big/powerful phones and it shouldn't be that different going from my thunderbolt to my Razr, right? Is there a website or some way I can look up the exact voltage or whatever each phone requires to charge and the voltage each charger puts out? Thanks.