'99 Johnson 200 overcharging?

I'm new hereand would appreciate any guidance. I have a 1999 Johnson 200 (J200PXEEN)on my 21' Grady White. The voltage gauge is reading 18+ volts atanything above idle and not much less at idle. I have dual, maintenancefree, deep cycle batteries that can either be run in "both" (which Inormally do) or either battery individually. I just replaced one ofthe batteries that was completely dead. I originally suspected that itwas charging high because of the dead battery, but it still reads high nowafter it was replaced. I am concerned that I might nothave noticed the high rate of charge and that led to the batteryfrying. On the other hand, maybe it was just time for the batteryto fail, and I have bad voltage gauge...
My questions are: How can I trouble shoot this? Can I just put a voltagemultimeter across the leads to the voltage gauge? If it is still18+ volts, do I have a bad voltage regulator? I have researched them-arethere differences between OEM and aftermarket? How difficult is it toreplace? Advice on replacing it? Thank you in advance!

It sounds like it is not regulating. The whole system is pretty simple; the stator yellow leads supply AC voltage to the reg/rect, and the output is fed to the batteries out on a red wire attached at the starter solenoid (battery pos cable side).

You should be Ok with a CDI part. I probably would not use any other aftermarket brands for this part. CDI seems reliable.

Replacing it is not really hard. It is more tedious than hard.
First of all, it is a water cooled reg/rect located on top of the block, behind the flywheel, and under the powerpack.
That is the issue. Removing the powerpack and replacing it with all those wires tucked back in their proper place is tough.

When you take the pack off, note the positioning of the large black rubber plugs that connect to wires going up to the stator. They fit in U shaped cutouts only one way. They will lock in place when you have them right.
Also, the various loose wires under there....all are color coded so just match the colors. Be very careful when bolting the pack back down that you don't pinch any wires between the fastening bolts and the pack or frame it mounts to.
Very easy to pinch those wires. Also, don't forget to re-attach the grounds that you will find under the right stbd mounting nut.

Clean gasket surface as required, install gasket, new reg/rect, six screws hold it down. It is possible to have a water leak there, so be sure you do the gasketing job properly.

Since it is water cooled, any air bubbles introduced into the cooling system thru a set of ear muffs for example, will cause that reg/rect to overheat and fail.
I never run that style of motor (loopers from 1990 - 2001) without the LU in a tub of water.
I have a 100 gallon stock tank, and I thought I was safe. Started engine, idle speed, shifted to forward, and let it run. It was churning water, and aerated that water up very, very fast. Reg/rect blew in less than 3 minutes, even tho the water in the tank remained at sufficient depth to pump.

Easy but tedious.

You can check it with a multimeter to make sure the gauge isn't wrong. With the engine running, just probe the pos/neg posts and see what you're getting.

Thank you gentlemen--fantastic information. My marina is having work done on the ramps, so tomorrow I'll have them put the boat on a rack and I'll take a good look, and use a multimeter to check different static voltages. I won't run it though based on your good advice. Also, I had heard that I may have to take the fly wheel off. "Daselbee"-- are you saying that that's not necessary? I'll order the VR tomorrow. Thanks again!

To change the reg/rect you do not have to remove the flywheel.

The powerpack has to be maneuverd skillfully back into place under the rim of the flywheel, but it is not hard, if you have the wires tucked properly.

It is going to be tedious for a first-timer to do....

Thank you again! If you're ever near the Loggerhead Marina in Lantana Fl, the beers are on me...