I have an old iPhone 3 , I changed the charging port as some of the pins were bent back. I purchased an inline amp meter and when I plugged it in it read 0.5 amps at 5 volts. It boots to the apple logo and charges for around ten seconds before shutting down . The back light remains on and you can faintly see the apple logo . At this point the amperage goes back to zero. Would I just have to get a fresh battery ?? Or would it be a mb problem??