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First, a fully charged 12v battery, at rest, not fresh off a charger, should read 12.4 to 12.5 volts, not 13+. That would indicate a faulty meter. And yes 17.6+ is too high. Make sure it is the correct voltage, then check your rectifier ground. Also temperature should have very little effect on voltage so testing in the cold is fine.
 

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Discussion Starter · #22 ·
First, a fully charged 12v battery, at rest, not fresh off a charger, should read 12.4 to 12.5 volts, not 13+. That would indicate a faulty meter. And yes 17.6+ is too high. Make sure it is the correct voltage, then check your rectifier ground. Also temperature should have very little effect on voltage so testing in the cold is fine.
The 13+v was with the 35amp/hr AGM battery that I put in there. It's one of these:


It appears 13+v is per spec and was verified by 3 meters. The charging voltage did settle down.
 

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If, while your tractor is running, the voltage on the battery is below 13.8V or more than 14.3V your charging system isn't right. Can you confirm the voltage you measured on the battery while the tractor is idling? Doesn't matter cold or warm engine.
 

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My 444 has a generator-starter and I've worked on way more cars & trucks w/ alternators. All having regulators inside them. With that being said, every 12v system I've worked on all had around 14.1-14.8v running. If battery is low it may jump up a little higher but if battery has been charged and you don't have all those lights on it shouldn't be charging at 17-18v as that will boil off all the water in the battery. That's something else you need to check is water level in that battery. Distilled is best. Don't use tap water to top off if low.
 
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