Originally Posted by Topp dawg
I have a newer tach that is digital. I don't see how this method could be accomplished.
Well, your newer tach surely has 12V + and - and the majority of tachs are not checking for RPMS, they're checking for voltage.
Hook up a trickle charger to the appropriate stubs for an hour and see if it counts up. If it does, leave the trickle charger on until you're synced up.