Battery Issue for a Dummy

[HappyPlace]

I need help understanding my twelve volt battery system. I will publicly admit, I don't know very much about it or the inverter. I had a Victron battery monitor (BMV-702) installed on our 2014 R31 CB, because I wanted to know the state of our batteries at any given time and the consumed amp hours for obvious reasons.

The other night while out on anchor, I opened the Victron monitor on my phone app to get a baseline on our system. It read as follows:

10/14/17 - 1850hrs.
10.83V (-9.50A)
State or charge: 99%
Consumed amp hours: -7Ah
Time remaining: 1d 5h


The next morning I checked again and it read as follows :

10/15/17 - 0752hrs.
10.15V (-3.10A)
State of charge: 90%
Consumed amp hours: -62Ah
Time remaining: 3d 19h


Now, I understand that the first reading indicated the batteries were almost fully charged at 99% (more to follow) and we were utilizing more amps at that time. So throughout the night we utilized less amps, totaling 55Ah.

What I cannot figure out is why the monitor is reading 10.83 and 10.15 to begin with? Wouldn't they be "dead" at this voltage. So, I squeeze my 6'-2" self in the lazarette compartment with my voltmeter to see if there is a loose connection and/or determine what the battery reads at the terminal. The voltage jumped up a little, but the First Mate confirmed it at 11.40V. Still almost dead, just 10% of a full charge. Everything running on the 12 volt system seemed to be working properly, with the exception of the dinette dimming LED light. (Could be unrelated.)

What am I missing here?
Is the monitor only testing one battery?
Could one of the four house batteries be bad?
If so, can you replace just one?
Would my equipment on the 12 V system still operate at these voltages?
How do you test the batteries individually since they are connected in series?

Very confused,

Al Sr.

 

[Red Raven]

I have a Xantrex monitor and not a Victron so I don’t know how similar they are. On mine the SOC is determined by the amp hours used (via coulomb count across the shunt) since synchronization (calibration) at full SOC. It looks to me that your system has not be calibrated. It should do this automatically once you bring it up to full charge. There also should be a manual option. Look in the manual. The SOC on these monitors typically cannot be trusted unless regularly calibrated. The voltage and current however can be trusted (if using a current shunt).

In any case, the SOC given by the system should always be checked against the battery voltage to make sure things look right. If they don’t agree resynchronization (recalibration) is due. No matter what the other numbers say you should try to not let your batteries get below 12.2volts (50% SOC) as the life is shortened each time you do.

As to your other questions: The house batteries are connected as a set in parallel (not in series) and are charged and discharged as one. To test them individually you need to disconnect them from each other and test the one at a time. It is possible only one is bad but unlikely, they have all seen the same environment and likely will go bad as a set if they have been abused. Most equipment will operate down to very low voltages as long as they can get the current they need. To confirm, if you run the toilet flush or another high current item you will likely notice slow or no operation when at low battery SOC.

Curt

 

[Levitation]

As I read this it is not 100% clear what the VOM read for voltage at the batteries. Did the VOM in your hand show 11.4 volts?
forget the fancy state of charge panel - it is totally messed up

Everything I am going to say here is predicated on the VOM showing less than 12.2vdc at the battery terminals
1. Turn off the invertor/charger at the AC panel - turn off the invertor - turn off ALL THE DC loads - do it now to save the battery set
2. Beg/borrow/buy a charger. Anything from a 6 amp to to the biggest you can lay your hands on and use it to charge your battery set
3. Pay the money to have a boat mechanic look at the invertor and see if a fuse is blown / switch is off / batteries are ruined / pedestal 220ac power is messed up, etc.

 

[knotflying]

This is kind of why I like to keep it simple. Sought of on Denny's vein, I would want to know what voltage you are getting using the multi-meter at the batteries. This would bypass all of your fancy equipment. If you are getting a good reading right at the batteries make sure (as you attempted to do) that all connections are clean and good. After that, if your equipment is reading differently than the voltmeter, start reading your directions for your unit.
If your batteries are weak then you need to figure out why. It could be a bad battery in the bank so I would load test each one separately. This is done after they have been fully charged and rested for about a half hour or so and are disconnected from one another. I am assuming your batteries are AGM or maintenance free so you cannot check any of the cells with a hydrometer. A couple of bad cells will drain all the batteries.
Additionally, unless you are using 110v items you should not leave your inverter on. The inverter running will provide a small drain.

 

[bill46]

Either your batteries are bad or Victron not calibrated. Cannot be 99 % under 12.8. First step is testing at battery with good voltmeter. Then fully charge batteries. Charger should get over 14, then drop to 13 something depending on temperature. Should be over 12.8 charged with charger off. Discharging below 12 will shorten life. That said I just replaced all 4 house on my 2014 R31. Believe they were abused by first owner. Upon removing found they said replace every 3-5 years, pretty short for AGM, but OEM were Chinese. I replaced with Duracell 31s made by West Penn in USA. Hoping for much longer life with care.

 

[HappyPlace]

Thank you all for the input,

We have OEM AGM batteries from China. We are thinking one or more of them are bad. The boat is being pulled out in another week or two, so we decided to load test them once it is on the hard. Looks like we will be replacing the four house bank. Happy Place is not that happy about replacing three year old batteries.

AL Sr.

 

[knotflying]

Thank you all for the input,

We have OEM AGM batteries from China. We are thinking one or more of them are bad. The boat is being pulled out in another week or two, so we decided to load test them once it is on the hard. Looks like we will be replacing the four house bank. Happy Place is not that happy about replacing three year old batteries.

AL Sr.

Here I go again! AGM are a good application on boats that heal a lot, like sailboats or when there is a need to mount them on their sides do to space limitations. However, IMO, there is always the human factor of destroying batteries. AGM's, although more rugged, are susceptible to being ruined just as any other battery. You can buy a flooded for about $90.00 and replace it every three years for 9 years and still come out ahead of buying one set of AGM. Just something to think about. Yes, I add distilled water about every three months. Just another periodic maintenance item to add to the list.

 

[Jim and Jackie]

In my last boat (it healed a lot) I had had both flooded, Rolls T250 and 2volt, and Lifeline AGMs over it's life.. The AGMs were the best I ever had they maintained a higher voltage and they were faster to recharge. Had them for 6 years before I sold the boat and were still performing. I will agree they ain't cheap. Maybe Al Sr.'s problem is the brand of AGM. My research and a good friend's ,who is in the marine electrical business got, us both to choose Lifelines.

It comes down to what works for you.

Jim Demerest
2010 R 29 Chessie

 

[bakerboat]

I think I've talked about this previously but any engine equipped with an OEM alternator is not really suitable for charging AGM/Gel batteries. AGM/Gel batteries need a different charge profile than lead-acid which are typically what are used with automotive style alternators. The end result is that AGM/Gel batteries are chronically undercharged using an OEM alternator which will shorten their useful life. More on the subject can be read here: http://www.pbase.com/mainecruising/auto ... _batteries