I've seen 100V+ on an unloaded outboard stator, revving the engine. I don't recommend holding onto them and doing that! Obviously there's a point where the stator would develop so much voltage that potentially it could exceed the insulation resistance value of the windings, and Zap there goes the stator!
The main concern on a Merc charging stator is to check the resistance and if it meets specs, it's probably OK. Check the leads' insulation for cracks, etc and repair as needed.
Now, when the stator is hooked up to a rectifier and loaded-up with a battery, that's a much different thing. The stator is rated for around 10 amps output, and this is dependent upon rpm (the old, unregulated-style of electrical generation).
An old unregulated charging system can be upgraded with either a separate voltage regulator, or a combination regulator/rectifier, which is what was used on most of the larger, later-model Merc outboards. This provides a much more stable voltage for sensitive instruments. An unregulated system can potentially drive battery voltages up to 15 or 16+ volts.
If you're just using the electric start on the motor and have no other electrical loads, you really don't need the regulator unless you're using a special-type battery. The old lead-acid batteries usually work OK with the unregulated system, but newer ones, such as the AGM-type, may not tolerate it.
Well, that's a lot more than your original question asked, but there it is!
HTH & have fun................ed
