Starting Battery dead after one night on the hook

PocoLoco

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Joined
Feb 24, 2018
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5
Fluid Motion Model
R-21 EC
2017 Cutwater 28. Relatively new starting battery (this is the second time this has happened. After the first time I replaced the starting battery). We're on the hook very seldom. We're snowbirds ... until mid April the boat spent the previous six months connected to shore power with the battery charger on. Anchored out last night for the first time recently. Overnite the house batteries were used minimally (fridge, charging cell phones, etc.). We have a Victron Connect monitor for the house bank. This showed the house bank at 85% just before I tried to start the engine this morning, which just barely cranked but not enough to start. It did start (happily) with the crossover switch turned on, but just barely. On the assumption that the battery is OK, what might have caused it to discharge overnite? A defective ACR maybe? Any ideas on how to figure this out? What would be the downside of totally disconnecting the starting battery when the engine is off, like with a switch on its ground cable? Thanks!
 
I’m not the smartest guy when it comes to electronics, but we don’t know the whole story and somebody else here will be asking these same questions. How old is the battery, really? How many times has it been drained down? It sounds like you replace just the starter battery and others here will tell you when have a bad battery, you need to change all of them so was that done? And how old are the other batteries? Did you switch the starter battery off? Then if you didn’t, did you leave anything on during the night? Hopefully once you answer these questions someone else will chime in and give you better info.
 
PocoLoco":1ch497cx said:
2017 Cutwater 28. Relatively new starting battery (this is the second time this has happened. After the first time I replaced the starting battery). We're on the hook very seldom. We're snowbirds ... until mid April the boat spent the previous six months connected to shore power with the battery charger on. Anchored out last night for the first time recently. Overnite the house batteries were used minimally (fridge, charging cell phones, etc.). We have a Victron Connect monitor for the house bank. This showed the house bank at 85% just before I tried to start the engine this morning, which just barely cranked but not enough to start. It did start (happily) with the crossover switch turned on, but just barely. On the assumption that the battery is OK, what might have caused it to discharge overnite? A defective ACR maybe? Any ideas on how to figure this out? What would be the downside of totally disconnecting the starting battery when the engine is off, like with a switch on its ground cable? Thanks!
Where does the 24x7 loads get power from? I know some early models R27-OB’s (2018 and 2019’s) had their 24x7 loads come off the engine battery instead of the house bank.


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Another 2017 C-28 owner here. The original factory installed Universal Power UB121100 AGM Group 31 deep cycle battery went 5 years before we replaced it just after purchase in 11/22. Replaced with a true AGM starter type Group 31 battery with 1150 CCA.
We have never let any of our battery banks go below 70 percent even when on the hook at the same anchorage for 2-3 nights. A big solar panel (335 watts) and good controller help. We have a Victron Energy Smart Battery Sense monitor on all four batteries to keep informed as to their individual status.
If I was having an unexplained draw down battery issue with either the house or thruster I’d make sure the Engine and Thruster rotary switches were turned off right after setting anchor.
If you look at page 31 and 32 of the C-28 owners manual, a few of the always on circuits are from the house bank but most are tied to the thruster bank. Unfortunately, a lot of our FM boats are “custom built” where the wiring reality doesn’t match the schematics.
Good luck hunting your gremlin!
 
Thanks rheimb1. All batteries were replaced. My question is, though, on the assumption that the battery is ok, what would cause it to be drawn down overnite on the hook, especially if the house battery is working normally and is not drawn down beyond 85%? For example, does the inverter draw from it? Could the ACR or wiring be defective? Anyone heard of this problem? Would putting in a swich to totally isolate the starting battery cause problems? It appears that the thing is not isolated, even when it's switch is turned off.
 
Propane solenoid is on engine battery. Make sure it is off. I’m not sure about bilge pumps.

Also I’m not convinced the acrs really help with the standard solar controller later in the evening if swinging at anchor. I’ve posted about this.
 
How many connections does the positive post of your engine battery have? Have you identified all of them?


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Good question. I shall work on figuring out what is connected directly to the battery. Any reason not to connect the propane solenoid and bilge pumps to the house or thruster battery?
 
Referencing the C-28 owners manual, it shows that the 24x7 power to the bilge pumps, the CO monitors and the bilge alarm come off off the thruster battery. The stereo memory and LPG switch are coming off the house battery. It does not (as I can find) show any 24x7 type leads coming off the engine battery. I do have a retired-in-place (dead) lead coming off the engine battery to the original (now removed) Morningstar solar controller.
There are, of course leads coming off all banks for the ACRs and rotary On/Off switches.
 
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