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First time boat owner... Battery alarm

May 27, 2021
52
Beneteau 37 Chesapeake Bay
I recently bought a 2009 Beneteau 37. We went out to dinner and when we came back, the panel was sounding an alarm. I couldn't really see which battery it was, but when I looked it was showing 15v. I turned off the charger and the alarm went away. Any ideas where to start? The engine battery is brand new but the house batteries (I believe there are two) are quite old and the broker recommended they be replaced but they seemed to be functioning fine. No idea where to start.
 
May 17, 2004
3,433
Beneteau Oceanis 37 LE Havre de Grace
What type of charger do you have? Does it appear to have any settings for temperature compensation? We have a Xantrex Trucharge 2, and if I set that to cold it sometimes boosts the voltage enough to throw that alarm. Also, what kind of batteries are they, flooded, AGM, or Gel?
 
Sep 25, 2008
6,272
Alden 50 Sarasota, Florida
The engine battery is brand new but the house batteries (I believe there are two) are quite old .
Therein lies your problem (or at least the first clue).

Your charger apparently can't differentiate old from new and may not differentiate low from fully charged, particularly when interconnected and all charging concurrently. Depends on which charger.

The charger may be seeing the low voltage from the old batteries which can cook the new one because it thinks they all need to be recharged when one doesn't... Hence the recommendation to never mix old and new batteries.
 
May 27, 2021
52
Beneteau 37 Chesapeake Bay
Therein lies your problem (or at least the first clue).

Your charger apparently can't differentiate old from new and may not differentiate low from fully charged, particularly when interconnected and all charging concurrently. Depends on which charger.

The charger may be seeing the low voltage from the old batteries which can cook the new one because it thinks they all need to be recharged when one doesn't... Hence the recommendation to never mix old and new batteries.
Really? Shouldn't the charger be able to charge batteries independently? What would you suggest I do until I can replace the house batteries?
 

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Sep 25, 2008
6,272
Alden 50 Sarasota, Florida
Really? Shouldn't the charger be able to charge batteries independently? What would you suggest I do until I can replace the house batteries?
It should but “should of, would of, could of”...

Look at the separate battery terminals with a voltmeter. That will tell you what is actually happening.
 
May 27, 2021
52
Beneteau 37 Chesapeake Bay
As an update, we were on the boat the rest of Saturday, through Sunday morning. The alarm didn't sound again. I kept checking the voltage the house batteries were usually around 13.2v and the starter batter around 13.8v, although both fluctuated. The highest I saw on the starter batter was 14.3v. I guess I'll replace the house batteries and see if that solves it. I guess I should also switch the charger from Gel to AGM. Does anyone know what the implications are of charging AGM batteries with the switch on the charger set to Gel?
 
Oct 22, 2014
15,863
CAL 35 Cruiser moored EVERETT WA
Simultaneous Three-Battery Bank Charging
Truecharge+ has three separate DC positive terminals to allow charging of three separate batteries (or battery banks). The total current into the batteries is a maximum of either 20 amperes or 40 amperes, depending on the model, which is divided amongst the batteries according to their state of discharge.
Note: The three outputs are not independently voltage regulated so it is important to avoid systems with mixed types of batteries

I have not played with the Xantrex charger. The above is from the manual. Which you can find here. http://www.xantrex.com/documents/Discontinued-Products/TC20_40(445-0050-01-01_Rev-A).pdf
If you have AGM batteries you will want to use an AGM profile. Make sure you identify the battery. Make sure you identify the way your battery system is wired. It sounds like this is a new boat to you. Congrats. Previous Owners have been known to modify (improve) their boats after buying them. Identify what you have and how it is wired before altering things.

For sure the selector on the charger should be set to meet the requirements of the batteries you have on board.
 
May 17, 2004
3,433
Beneteau Oceanis 37 LE Havre de Grace
As an update, we were on the boat the rest of Saturday, through Sunday morning. The alarm didn't sound again. I kept checking the voltage the house batteries were usually around 13.2v and the starter batter around 13.8v, although both fluctuated. The highest I saw on the starter batter was 14.3v. I guess I'll replace the house batteries and see if that solves it. I guess I should also switch the charger from Gel to AGM. Does anyone know what the implications are of charging AGM batteries with the switch on the charger set to Gel?
Here are the output voltages for your charger -
1627307638486.png


The Gel float voltage is a little high for AGM’s, which wouldn’t be great for their longevity. The table also matches your measured voltage of 13.8 for the start battery and ~13.2 for the house - since the house is often under load it may float a little below the target 13.8.

The alarm may have been triggered if the charger went from float to absorption mode. I know the Truecharge 2 does that every week for at least a few minutes; maybe the original Truecharge has a similar process. The absorption voltages, at least at “warm” should all be under the alarm threshold of 14.75, but maybe there was some kind of temporary fluctuation. Or maybe it targets the absorption voltages in the chart for the lower (house) bank, driving the engine bank up higher.
 
May 27, 2021
52
Beneteau 37 Chesapeake Bay
Thanks everyone... I switched to AGM and confirmed that all 3 are AGM. As I said earlier, the house batteries are older and need to be replaced. It sounds like the voltage of that battery may be dropping and causing the newer starter battery to spike. When I was on the boat today, the house batteries were at 12.8v, which seems incorrect.

Until I get new batteries, should I turn off the starter battery to prevent it from overcharging? I don't want to turn off the house batteries since they are needed for the fridge, bilge pump, etc.
 
May 17, 2004
3,433
Beneteau Oceanis 37 LE Havre de Grace
Are you going by battery voltages reported on the DC panel or measuring with a volt meter directly on the batteries? We have some voltage drop between the batteries and the panel, so even though the panel often reads 12.8-13.3 (depending on loads) the house batteries are actually at 13.2-13.4. If the bank is actually at the higher level then I wouldn’t use that as a signal of battery health.

Also, if yours is wired like mine the charger connects to the battery side of the switches, so even if you turn the switches off the batteries still get charged. Now that you’ve switched the charger to AGM I wouldn’t worry about overcharging the start bank. The charger should float at an OK voltage for it.
 
May 27, 2021
52
Beneteau 37 Chesapeake Bay
Are you going by battery voltages reported on the DC panel or measuring with a volt meter directly on the batteries? We have some voltage drop between the batteries and the panel, so even though the panel often reads 12.8-13.3 (depending on loads) the house batteries are actually at 13.2-13.4. If the bank is actually at the higher level then I wouldn’t use that as a signal of battery health.

Also, if yours is wired like mine the charger connects to the battery side of the switches, so even if you turn the switches off the batteries still get charged. Now that you’ve switched the charger to AGM I wouldn’t worry about overcharging the start bank. The charger should float at an OK voltage for it.
Thanks for all your help. So do you suggest I hold off on replacing the house batteries? They are substantially older than the starter battery.
 
May 17, 2004
3,433
Beneteau Oceanis 37 LE Havre de Grace
Thanks for all your help. So do you suggest I hold off on replacing the house batteries? They are substantially older than the starter battery.
I think they might or might not be serviceable, but the voltage at the panel while on the charger isn’t a great indicator. The “real” way to find out is a 20 hour load test like Maine Sail describes at How do I test AGM batteries for damage from overcharge? or I did at 20 hour battery capacity test done. That’s a test that’s easier to do in the winter when time is less of a problem. You could probably get some idea of health by leaving the charger off overnight or for a daysail and checking battery voltage afterward.
 
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Jan 7, 2011
2,833
Oday 322 East Chicago, IN
I knew my old batteries (FLA) were dying when I could watch the voltage drop from 13+ to 10.something on a 2 hour sail. I held my breath hoping there was enough juice to start the Yanny. I had 2 batteries (group 27) and I would only use 1 as the house and keep the other one to start the engine if needed.

I upgraded to 2 6-volt GC batteries in series. Voltage at my CP stays pretty consistent 12.2 while sailing now and I feel much more comfortable. I still need to add a starting battery, but I am not holding my breath each sail now.

I probably (no, definitely) shortened the life of my 5-year old group 27’s by not checking the water levels. Checked them one time last year and saw a lot of the plates showing :facepalm:…my bad.

Check the new 6-volt batts every month now.

Greg