House SOC while on shore power

D

Decisions

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Nov 23, 2025
4
Beneteau Oceanis 41 San Diego
Hi all,

Newbie here but I am out of ideas and hope you can help. I have a 2024 Oceanis 40.1. While on shore power the House SOC continuously drains 1% to 2% a day. I thought this might be a battery preservation program but apparently not. I have seen it drain all the way to 30%. If I start the engine it charges right up and then drains right back down. I have asked our maintenance team and they have asked Beneteau but just crickets. I think there is a miswiring in the converter or perhaps a short somewhere. We have lost a couple of house breakers that have been replaced under warranty but I think something else is going on.

any ideas?

Thanks all!

Dan
 

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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,792
CAL 35 Cruiser #21 moored EVERETT WA
Welcome Dan to the SBO forum and your new boat.
  1. What type of batteries do you have for your house?
  2. While on Shore Power, do you have the charger turned on?
  3. Do you have a bilge pump? Is to pumping water out of the boat?
 
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D

Decisions

.
Nov 23, 2025
4
Beneteau Oceanis 41 San Diego
Hi!

I have epsilon super b lithium batteries.

I thought the battery charger was automatic on shore power? Will research.
edit: I am not at the boat but your question made me wonder if the batteries ever get charged off shore power. I honestly don’t know and it may be because the source is set wrong on the boat. <head smack> will check next week.

Yes on the bilge pump but the bilge is bone dry and I don’t think that is the issue.
 
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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,792
CAL 35 Cruiser #21 moored EVERETT WA
Lithium batteries can have a 1% parasitic discharge. You will need to check with the specific battery manufacturer. This usually is not a problem with large battery banks. It is dealt with by regular charging. If your charging system is not on while attached to shore power, you may resolve the issue by correcting that problem.
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,435
Hunter 310 West Vancouver, B.C.
@Decisions , by your chart it looks as if there is a periodic discharge of ~1% SOC which occurs every ~1.2 days in a very short period of time, maybe one minute or less. Assuming that the representation of the chart is proportional to the electrical discharge.

1764044969074.png


Don't know the size of your battery bank so can't say how many amps this represents but it's fairly large. Of course your batteries are not being charged at this time.

I can only suggest you invest some time in looking for this source of heavy discharge. Sorry, but I can't imagine what the load might be. Bilge pump maybe ?

Hook up the charger to your batteries and see if this phenomenon disappears. If it doesn't, write back. Doesn't tell you WHAT is pulling the amps but puts you back to the correct operation.
 
D

Decisions

.
Nov 23, 2025
4
Beneteau Oceanis 41 San Diego
That’s 1% per day more or less, and I am not sure why the drop off. It almost feels scripted. The date scale is at the bottom, and you will note that it is from 16 Nov - 23 Nov. I appreciate the direction. Ultimately there isn’t anything terribly mysterious about this. Battery’s are draining and the shore power isn’t charging. A volt meter should tell me what’s up. I will let you all know what I find out. Won’t be back on the boat until about 10 Dec.

Thank you!
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,435
Hunter 310 West Vancouver, B.C.
Decisions said:
Battery’s are draining
Click to expand
It's the "WAY" the batteries are draining that will tell the tale & your shore powered battery charger isn't connected to your batteries.

Other than that, every thing else looks normal.
 
D

Decisions

.
Nov 23, 2025
4
Beneteau Oceanis 41 San Diego
Hi everyone. I think I have figured it out. We have a cristec battery charger that is responsible for maintaining the bow thruster battery, house batteries and the engine battery. This charger is great but it can’t tell what type of battery it is charging. So, it is currently set up to charge agm batteries and not lithium batteries. which means the lithium batteries (which like to charge at 14.4v) never get any juice. Cristec says not to mix battery types and of course that’s where we are. So probably a second charger that maintains the house batteries and one dedicated to bow thruster and engine. Alternative is to just make engine and bow thrusters lithium and reconfigure the charger. either way works.

thanks all!
 
Davidasailor26

Davidasailor26

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May 17, 2004
5,896
Beneteau Oceanis 37 Havre de Grace
Decisions said:
Hi everyone. I think I have figured it out. We have a cristec battery charger that is responsible for maintaining the bow thruster battery, house batteries and the engine battery. This charger is great but it can’t tell what type of battery it is charging. So, it is currently set up to charge agm batteries and not lithium batteries. which means the lithium batteries (which like to charge at 14.4v) never get any juice. Cristec says not to mix battery types and of course that’s where we are. So probably a second charger that maintains the house batteries and one dedicated to bow thruster and engine. Alternative is to just make engine and bow thrusters lithium and reconfigure the charger. either way works.

thanks all!
Click to expand
The AGM charge voltage is probably pretty close to 14.4. The charger should be set to output something pretty close to that. Maybe if the charger is set too high it might be over the maximum cutoff voltage of the lithium’s BMS causing it to disconnect itself from the charger, but I’d be surprised if that were the case. Can you tell what voltage the charger is actually putting out to the banks, by multimeter?
 
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Likes: jssailem
D

dlochner

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Jan 11, 2014
13,449
Sabre 362 113 Fair Haven, NY
Decisions said:
Alternative is to just make engine and bow thrusters lithium and reconfigure the charger. either way works.
Click to expand
It is probably better to keep these batteries as AGM batteries because LFP batteries that can support high inrush currents are fairly rare. If you still have the original OEM alternator, it is not set up to charge LFP batteries. AGMs work for start batteries because they are recharged quickly and are maintained at 100% SOC, relying on shore charging for the AGMs would lead to more time in PSOC which is deadly to AGMs.

Depending on your sailing plans, it may be time to rethink the whole electrical system to make it more efficient and to keep every thing charged appropriately.
 
Tally Ho

Tally Ho

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Jan 7, 2011
5,858
Oday 322 East Chicago, IN
When I added LFP bank of house batteries last year and kept a sealed lead acid battery for starting the engine, I added a second battery charger from Victron, suitable for charging the LFP bank. The old Guest charger just charges the starter battery.

Greg
 
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