Not exactly sure if the device / component or setup I'm asking about even exists. But, here is my naive question (I am bad with electrical in general):
Is there something built into modern vehicle electrical systems which prevents reverse flow of power from the components plugged into the accessory outlets (cigar lighters)? Can that device go bad in such a way that the vehicle actually draws power from say my tablet plugged into the 12v receptacle in the event of lower voltage?
Vehicle: 2002, Excursion with the 7.3 PSD
Reason for question: We seemed to experience a situation recently where this vehicle was draining several Apple devices that were plugged in while driving. In fact, the only thing that caused me to pull over and plug in my diagnostic tester was my spouse telling me something was wrong beyond just not-charging. Voltage was noticeably low and continuously dropping. Previous owner did a poor install on new alternator cable (didn't solder it to the copper eyelet, but just crimped and it had come loose). Fixed, on our way and no big deal but when I told this story to a diesel mechanic friend of mine, he stated that it was impossible the vehicle was draining the devices and that they were just not-charging. Maybe that's the case, but sure seemed like they were being drained in short order. Plausible or no?