Re: 1996 150 hp volt meter reading
On that engine you surely have a regulator. Regulators have limits and they are dependent upon a load....i.e. a battery wired to the regulator. As Old said, a bad wiring connection down circuit from the regulator could disconnect the battery from it, temporarily or whatever, and as a result spikes in the voltage would be the result.
On what he said about shiny, what's outside doesn't really matter. It's shiny on the inside, terminal to terminal metal to metal, where the current transfers is what matters. Get them all, at the battery and at the engine ground on the engine block and red distribution point....don't remember on that engine, usually the input hot lead to the starting solenoid.
Additionally, pull the pins from the sockets for the wiring to the regulator and clean that up too. A little WD-40 and mating of connectors a few times each will clean them up.
Mark