Get a portable "instant" charger pack online for about $40. Charge it and take it along. It can also charge your cell phone or video equipment. Trickle charging from a vehicle outlet is just not going to do the job for many items.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
You need a portable "Laptop Car Charger".
This is a peculiar issue that most of the professionals face. I was also having same type of issue few months back with my Asus Chromebook. It was also discharging in 4-5 hours until i bought laptop car charger from PapaChina. They have some of the high quality laptop car charger at wholesale price.