I had this problem some years ago with a hefty HP Pavilion model. Billed as a great device for enjoying audio and video, great big screen for watching movies, but connected to an airplane power outlet, charging couldn't keep pace with use, even for less power-intensive activities such as working in Word and Excel. It was probably here on FT in this forum that someone explained to me that the computer needed more power than it could draw from the airplane outlet. Even on a fairly short trip, like Chicago to Washington DC, I was alarmed to see how quickly the battery ran down.
If you need to travel with a computer like that, the only solution seems to me to be to travel with a fully charged backup battery. And, as said before, turn it off at times and let it recharge, although if I recall correctly, the recharging will be slow.
My eventual solution was to leave that heavy HP Pavilion at home and make it my desktop computer. Its weight alone was killing my back, much less lugging a backup battery along.
I got a smaller, slower, lighter-weight HP Pavilion (what can I say? I was a fan at the time). Did I mention slow? It had a celery processor --- oops, I mean a Celeron processor -- hardly different. Bought a backup battery for it (dinky computer size meant dinky battery life), and that became my travel computer. I called the big one that stayed at home Dr. Evil, and I called the little one that went on trips with me MiniMe. Dr. Evil burned himself out years ago, his own fan couldn't keep him cool; MiniMe is still with me.