Ron, it's done all the time. Jump starting a 6 volt with a 12 volt. Just don't leave the 12 volt hooked up more the a few seconds. It might go boom!💥 The 6 volt battery that is. The starter doesn't care but the battery does.
🛠

Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)