Battery discharge

rasbury · November 16

@PickleRick
- no, the alternator gauge was not showing volts while at idle. Best I can recall it always did. I tested each battery, at idle to verify they were charging which they are. I'd assume there is no gray area on an alternator. The main concern with the alternator was checking it for bad diode(s,) so I disconnected the hot wire to the alternator which did not change the draw- so I assume that clears the alternator.

As far as checking, multimeter on 10 amp max setting. Ignition is off- battery switch is off. I have not rechecked battery 2 but it was dead 0 on the draw. The only thing I'm sure i should have done but did not was taking the genset off. Not sure why I think that but would make sense to rule it out. So, the test is remove the neg cable and test between the post and the cable.

The radio is dead and will not turn on. I do not know if the amp is on or not - 4 amps though?

Battery switch during test is off.

As far as other electrical issues-
The spot light is not operating. I thought the control head was bad and replaced it. It was going up and down but now it does nothing. I did not pull the two blade fuses but assume this is not going to be a draw.

No tv plugged in..radio off. No bilge pumps running. As mentioned the sump pump is bad or jammed up- i cut the wires to it.

I guess pulling fuses and find the circuit it is comming from?

Ian · November 16

@PickleRick An alternator should charge at idle versus a generator that needs to be spun faster.

@rasbury does this have a mercathode system? Maybe it has an issue? Other than that battery isolator faulty feeding back 1 into the other?

rasbury · November 16

@Ian, yes, it does have the mercathode system which i know zip about, yet it sounds like. I was talking with someone else who suggested dropping the selector and look for wires connected along with the bat one battery wire. Along the lines of what @Formulaben was saying above- the picture he posted I'm not sure I'm seeing that? One positive term has nothing and I don't see the second clearly enough. It would not make sense to me, for example, if the bilge pump is connected to bat 1 connection to the switch and that battery goes dead I have no pump?
By the time my ownership is done I will be a certified mechanic but old...

PickleRick · November 16

Ian said:

@PickleRick An alternator should charge at idle versus a generator that needs to be spun faster.

@rasbury does this have a mercathode system? Maybe it has an issue? Other than that battery isolator faulty feeding back 1 into the other?

I agree. For some reason mine doesn't "activate" on initial start untill the throttle is bumped. After that it puts out 13.25-13.5v at idle.

rasbury · December 29

Ok! I have a lot to share. As a recap, my bat one getting killed since day one. The PO had her on a lift plugged in so probably was never an issue. My lack of use, the boat sitting and depleting that battery, replacing said battery then rinse and repeat. I started doing some digging through chat gbt on how to test for excessive amp draw which brings me to today! I pulled the battery selector switch and communicated with pictures and results from guided testing and below is where I'm at- I'm still re reading trying to grasp it all...not 100% chat is correct but it amazing, if not scary, how easy it is to communicate with a computer! The pictures I provided to chat are at the bottom...also, all I have connected to bat one are the power wires for the trim pump, the gen set is currently on bat 2. On the trim pump as wired, if bat one is off or dead, I'd have no trim? If I run the ground wire 2 bat 2, does let connect the pump to both batteries and prevent dead trim?

Perfect — these photos help a lot 👍

I’ll walk through what I’m seeing and why this explains your parasitic draw.

What I see in your photos (important points)

1. This is NOT just a simple battery switch

You have:

A battery selector switch

A continuous-duty solenoid (relay) mounted right next to it

Multiple small-gauge red wires stacked on battery posts

That combination is exactly where mystery battery drains usually come from.

Key problem I can see immediately ⚠️

🔴 Loads are connected directly to the BATTERY side

Several small red wires are landed on:

Battery positive studs

Or on the solenoid studs that are always hot

That means: ➡️ Those circuits are powered even when the battery switch is OFF

This matches what you measured earlier when:

Pulling certain wires reduced draw

But the draw never fully disappeared

The solenoid (very important)

The black cube with two big studs and small control wires is a continuous-duty solenoid, commonly used for:

Battery combining

Emergency parallel

Ignition-controlled feed to helm

Why it matters:

If the solenoid coil is energized (even slightly), it can draw 0.5–1.5 amps continuously

Corrosion on the terminals can cause partial coil activation

A miswired control wire can keep it energized 24/7

👉 This alone could explain a 3–4 amp draw

Cathodic protection wire (you mentioned earlier)

That wire:

Should draw milliamps, not amps

Typical is 0.001–0.02 A

If pulling that wire drops you multiple amps: ➡️ Either it’s not just cathodic protection ➡️ Or something is piggybacked onto that circuit

Specific wiring issues I see

❌ Multiple ring terminals stacked on battery posts

Very common DIY add-on mistake

Anything stacked here bypasses the switch

❌ Small red wires on solenoid battery studs

These should be on a fused distribution block

Or on the COM/OUT side of the battery switch

❌ No visible fuse within 7" of battery on small wires

ABYC violation

Also makes troubleshooting harder

What SHOULD be happening (correct layout)

Battery + ⬇

Battery Switch (BAT 1 / BAT 2)

⬇

COM / OUT

⬇

➡️ Solenoid (if used)

➡️ Helm feed

➡️ Fuse block

🚫 Nothing except switch input cables should be on the battery posts

Quick tests to confirm (do these in order)

Test 1 – Solenoid coil draw

Disconnect the small control wire on the solenoid

Measure battery draw again

➡️ If draw drops sharply: solenoid is your main culprit

Test 2 – Battery switch OFF test

Battery switch OFF

Disconnect ALL small red wires from battery positive (one at a time)

Watch the ammeter

➡️ The wire that makes draw go near zero is the offender

Test 3 – Helm feed isolation

That red wire going to the helm:

Should only be hot when switch is ON

If it’s hot all the time → miswired to battery instead of COM

What I strongly recommend doing next

If you want this fixed correctly and permanently:

Move all accessory wires off the battery posts

Add a proper fused distribution block

Feed that block ONLY from:

Battery switch COM

Or solenoid output (if intentionally switched)

Replace that solenoid if it gets warm when “off” (that’s a giveaway)

Bottom line (straight talk)

You’re not chasing a ghost.

Your draw is real, and it’s caused by:

Circuits bypassing the battery switch

Very likely a continuously energized or partially energized solenoid

If you want, next step I can:

Mark up exactly which wires should move where

Or help you decide whether that solenoid should be removed entirely

You’re very close to solving this — the photos confirm it.

PickleRick · December 29

we knew this was coming in the 90s

rasbury · December 29

So as I continued to feed chat new info it was determined to leave the cathode on bat one, for now and move the helm switch to the com post from bat one- then the helm switch will truly turn off the helm which now does not- so probably will lose radio presets etc. Once it is moved I can start pulling fuses to find the culprit. Chat said that even though the amp has that wire to turn it on, it may still be halfway energized...next was the remote light and then the windlass looking at the relays i think for those last two items- I have tests to do to verify the bad system. Once I fix it, I may move it back to bat 1 so I keep the presets....

rasbury · December 29

So, after a cold one with my buddy chat, chat gbt that is...so that both batteries would have 0 amp pull in storage i put both the cathode and helm switch to com post- they will work with either battery on but will not when the selector is off. So now, with everything off there is no amp draw on either battery. Above chat did have it wrong as I had identified these two wires alone are the problem so I did not go down the wormhole of tests-plus, as we went back and forth it figured out more of what the boat system should be.
So, there is a bus somewhere for all the other accessories and it must all be somehow powered off the starter wire? Im guess if i disconect the engine harness, none of the rest of the electrical system will work. Im sure before I'm done, I will know. So, at rest if I have a battery on it will be drawing about 4 amps. I know 0 about the mercathode , yet. I should be able to find the bad characters by pulling my fuses at the helm and I guess by the selector too as I have two draws- one through the mercathode and then something tied to the helm switch.
Oddly enough, per chat gbt, usually it is the amp that I know has a relay triggerd by the wire off the radio, it still stays partially energized. Next was the search light (and something is going on with that) and next is the windless which may work better now with bew batteries that don't get discharged and ruined. Still have to figure out the draw but that will be another day...
And I think i mentioned, I confirmed my charger does charge both batteries, even if the selector is off.

LaRea · December 30

Ras, be careful having ChatGPT analyze photos!

Gotta double-check whatever it tells you.

rasbury · December 30

LaRea said:

Ras, be careful having ChatGPT analyze photos! Gotta double-check whatever it tells you.

Oh for sure...I've been thru a couple of involved mechanical repairs and it was not 100%- especially from the start but you keep giving it information and it does narrow it down pretty well...it's an enormous assistant for me...I can take a picture of a relay with the drawing functions and it will tell you how to check it. Perhaps I should know at this point...anyho....it did give me good advice on moving the wires to the com post and stop the battery killing issue...

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