The batteries you are jumping are probably so depleted that the jumper cables are trying to run a huge current into them. Better check them and get them charged up before going on. Your generator or shoreline should be charging them. Measure the voltage across them with one of those working.
Old sick batteries or trying to charge a bank of 6 batteries that are run down can put a huge load on an alternator and cause it to crater.
MAKE AND MODEL OF RV sure helps.
H/R Endeavor 2008
Ford F150 toad >Full Timers
Certified Senior Electronic Technician, Telecommunications Engineer, Telecommunications repair Service Center Owner, Original owner HR 2008