"If your engine is indeed a 19
"If your engine is indeed a 1984 Evinrude it would have one of the model numbers as follows: E or J 90MLCRD, 90LCCRD, or 90TXCRD.
Now, if you have Power/Tilt/Trim (PTT), you should have a 10 amp stator under your flywheel (OMC part # 582867--># 583672), in which case your engine should have a water cooled voltage regulator/rectifier assy located on top of the block, between the cyl heads, near the rear of the engine (OMC part # 582094--># 395391--># 395204)
If you do not have PTT, you should have a 6 amp stator under that flywheel (OMC part # 582016--># 583671), in which case a voltage regulator would not be used, but would rather use a small rectifier (OMC part # 582339--># 583408) located on the starboard (right) side of your engine near the terminal strip.
You can determine which stator your engine has by removing the flywheel. The part number will be imprinted on top of the stator, usually at the top front area. Be sure to torque that flywheel to 105 foot pounds when you reinstall it.
If you have the 6 amp stator combined with the small rectifier, do not be concerned with the voltage reading as the amperes are low. You can get a volt meter to read extremely high with a bunch of AAA flashlight batteries, but the amperes are not there. In short, that creates no problem.
However, if that stator is a 10 amp, and you have the small rectifier instead of the voltage regulator assy, that may create a problem somewhere in the future but it's not a certainty as I've seen many a engine with this type cross mix that have been running for years with no associated charging problems..... but it is a gamble.
Pertaining to what battery life you can expect. I have no idea and wish I did as I'd be able to predict when my car battery would fail....... again <sigh/grin>.
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