Batteries over charged under load help

Two Tides

New Member
Feb 10, 2017
7
Puget Sound
Boat Info
1997 370 Sundancer
Engines
Twin 3116's
Hi all, I have a 370 with 3116’s. I recently replaced the batteries as the old one were 6 years old and shot.

The boat had 4 29 series wet cell batteries. And I put in 4 AGM 31 series.

When I am underway at about 1000 rpm - the colts shout up to 16. If I turn a lot of stuff on (lights, reddot heat, amp etc) the colts go back to the 13’s.

My question is’ what causes this? Is it my battery charger (have stock one), are the batteries too big. Has anyone else see this or had this happen?

Would love any help
 
Your battery charger should not be a factor when underway unless you are running the generator. More likely you have an alternator that is not regulating properly or your gages are lying to you. I have found my dash gages to be "advisory" at best. Next trip out, You might try hooking up a DVM to to see what's really going on.

Either way, a bigger battery just denotes higher reserve capacity, so no, your batteries are not too big.
 
I've had the same issue and it was the alternator. The internal voltage regulator failed causing the high output.
 
Was that read on an analog needle gauge or digital gauge? id want to first verify at the batteries, especially if that was an analog gauge.
 
What was it reading with the old Flood batteries? Did one of your batteries have a bad cell? Old batteries tend to short out a cell and may take out a Vreg. Watch that overcharge thing on AGM's. They don't like it. I think Optima recommends 13-15Vdc. You should really check the Vdc with a DVM at the battery while the engine is running.
 

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