why would my van start to take a jump from other car and then suddenly stop?

Clean cable connections... IF that don't help.... Replace the battery!!!!

MAYBE after FULLY charging whatever battery you put in it , start it up and see if it's CHARGING or if you just read battery voltage???? ....KEY is to have a FULLY charged GOOD battery in it , otherwise checking while running , with just a voltmeter , may not be accurate.