My laptop battery is 10.8 volts. The charger I assume inverts ac to dc current to charge the battery. I also assume that if there are any ac voltage requirements in the laptop it must have an internal invertor from dc back to ac. The charger input is 110-240volts 1.7 amps. The output is 18.5 volts 3.5 amps. My question is why can't a 12 volt source like a jumper box be used to run the laptop, when the battery is low, through the port that the charger is plugged in when charging the battery. My thinking is that the battery being 10.8 volts dc is charged with up to 18.5 voltsdc then it would be safe to plug in a 12 volt battery source. Thanks for your time!