Battery Health Questions

[Rick D]

I have two banks of six-volts, and they are usually run parallel. I noticed in a recent day-sail that after about three hours, with frig and freezer running, instruments and radar on and some autopilot use, the voltage dropped under 12 at the panel meter. The Freedom remote was indicating 12. Here is what I did:Next time down, I turned off the charger and monitored the voltage at the panel input compared to the battery terminals hourly for 24 hours. The average draw was about 7-8 amps. At the end of 24 hours, the panel showed about 12.2 volts and the batteries about 12.45. On average, the panel volt meter showed about .3 less volts than at the terminals. I considered this to be about right for a 450 amp bank. What do you think? What about the spread from terminals to panel? I figured that was about right for a 15-20' run. Agree?Yesterday, in a six hour sail, the batteries registered about 11.2 volts, off from a full charge, with mostly standby on the radar and no autopilot use.Today, I turned the charger off after a full overnight charge and turned on a 17 amp DC draw for an hour. The panel indicated 11.5 volts. I checked the batteries at the terminal and they registered 12.45 volts. I checked the gravity of each cell and it was normal at 12.7 volts (DC draw off for 30 minutes). One was about .2 lower.. maybe.The batteries are on their third season. They are serviced regularly and have not had their plates exposed (always plenty of water). The terminals are clean and were freshened up last season. The batteries were equalized last season. There is an average 5 amp draw 24/7/365 on refrig and freezer. We also use the boat pretty heavily even while not out sailing. It has a three-stage Freedom charger/inverter that seems to be doing just what it is supposed to, and a Balmar three-stage regulator that may be, if anything, a little light on the bulk setting.So, I was about to replace the banks, but now am wondering if that is premature? My next step is to pull off all the terminals again and make them bright and see what if any change that makes. Beyond that, the only thing I can think to do is to take them somewhere to be load tested. Is that effective with a deep-cycle battery? I have only done that with starting batteries.Any better ideas? Comments? Guesses?Rick D.

 

[Bob F.]

Rick, my suggestion

is to do a load test on each battery. I'm not a battery expert by any means. On my H376 I have 2 4D's as my house, so its really easy to tell when one is bad. And I've considered going the 6v route next time. But perhaps if you have a bad battery in the group and its effecting the whole bank. Considering its a fairy new problem, maybe just one of the 6v's is bad.Also, I've read abt a product that you add to the the wet cell that is supposed to be a miracle cure for wet cell batteries. I cant remember the name, but they advertise in The Log sometimes.Good Luck. Bob

 

[Don]

Rick

Where did you measure the 11.2 v reading - at the batteries or the panel?If at the batteries, you likely have a bad cell or two; if at the panel, you likely have a bad connection someplace. Your elec system seems like a good design and the batteries are maintained properly from your description so you are right to start with the easy/cheap stuff like connections. A load test will work on ANY battery if you go that route.Don

 

[Rick D]

Don:

11.2 was indicated by the panel meter (slightly less than the reading at the meter connections). RD

 

[Fred Ficarra]

Rick, consider tossing the panel meter.

If you can't calibrate it to read the same as the voltage value obtained at the batteries. A reading of 11.2 is DEAD. Clearly your batteries are not dead. Separate each battery from each other with no load on them. (just like they are on the store shelf) Then check the voltage. If there is any difference then you can take them in for a load test. But first try to borrow the device from the battery shop. They might let you have it. But I'll bet your batteries are just fine.

 

[Don]

still not sure

I think the only precise way to tell is measure voltage at the battery terminals ignoring the panel meter. If you have a problem at the terminals, you know the rest of the story.A good surrogate load test is crank the engine on the house bank while measuring voltage drop at the battery terminals. anything more than approx .5V and they would likely fail a "real" load test. You might also want to pick up or borrow a hydrometer, particularly if you narrow the problem down to the batteries, to help ID which battery and which cell is/may be bad.Good luckDon

 

[Rick D]

Reply to Don's Suggestion

I agree with not putting much credence on the panel meter, but what got my attention is that the behavior seemed out of line with prior experience. I have a hydrometer and the cells seemed fine to me (one slightly off, but acceptable). RD