Depends on your onboard charger. If you have a single stage charger like the Magnetek/Parallax, it is crap. You are better off replacing it with a real converter/charger or using an external charger. If you have a modern 3 stage charger like a Progressive Dynamics (w/charge wizard), just let the onboard charger do the job.
I replaced my fully functional and operating Magnetek 7345 a few years ago with a Progressive Dynamics 4655 and am very happy.
Bobbo and Lin
2017 F-150 XLT 4x4 SuperCab w/Max Tow Package 3.5l EcoBoost V6
2017 Airstream Flying Cloud 23FB