Hello, I recently received a USB power pack but I can't seem to charge the dumb / feature phones that I have. When I use this adapter to connect the phones they say that they are charging but even after 5 hours they seem like they didn't get a charge t all. Is the voltage difference the issue? With the USB being 5V and the phone battery being 3.7V (though the output of the chargers that the phones came with is 5V). Could I have a faulty unit? I'm trying to find out what the mA rating of the USB port is but the supplied wall charger is 5V 400mA so if the USB port is providing less amps than that it won't charge properly? Also, because the battery in the power pack as well as the batteries in all the phones is 3.7V what would happen if I remove the USB port and wired that 10 in 1 adapter directly to the battery? Thanks for reading.