12V battery problems

Navicula · Sep 2, 2012

kbbarton said:
Hello all. I'm having problems charging my batteries and I am wondering if anyone else has had a similar issue. A few weeks ago I neglected to turn the battery selector on the breaker panel to "Off" before leaving for the week - I accidentally left the selector on "Both". Nothing on board was powered on, so there was no load whatsoever. However, the following weekend I came back and found both batteries completely discharged. Does that mean that there is a short somewhere?

I have a West Marine 30A charger, and every attempt at recharging the batteries has been met with some sort of fault code. One battery gives me an "internal short - cannot charge battery" code and the other one says "sulfated - cannot be recharged".

Has this happened to anyone and if so, any recommendation for correcting the problem (other than simply buying two new batteries)?

leftbrainstuff · Sep 2, 2012

The only true means of determining your battery state is by checking the specific gravity. I'm assuming they are flooded lead acid.

Jon_E · Sep 4, 2012

Turning off shore power before leaving the boat is not recommended. If you sprung a leak the bilge pump would draw down your batteries pretty quickly and your boat would totally flood. Secondly, in warm weather a fully charged battery loses 1% of its charge every day just sitting with no load. You want to keep the batteries topped off.

Back to your question: Do you have a short somewhere? That is one possibility. More likely is if one battery was already going bad, the bad battery destroyed the other since you left the selector on "both". Depending on how they were wired and the types of each battery, the good battery spent itself trying to charge the bad battery.

As you know, once a battery is fully drawn down it is ruined.

Maine Sail · Sep 4, 2012

Many "smart" battery chargers will not charge into a dead bank for safety reasons. A very low voltage can mean a shorted cell so charger makers give them a min voltage to charge into so a battey does not blow up. many solar controllers and wind controllers do the same.

You need to find an old "dumb" ferro charger like an old Century or similar brand car charger to get them above 11 volts. From there you can re-connect your "smarter" charger and re-charge them.

Turning off the battery switch is always recommended when leaving the boat as many of the devices can have parasitic loads and kill the bank.

Your bilge pump should always be direct wired to the bank with appropriate fusing and not go through the main battery switch..

As for taking specific gravity readings they are useful to determine the individual cell balance but beyond that it is just one way to spill acid and wreck clothes. A rested open circuit voltage reading will tell you state of charge quite accurately. The vast majority of the people I find out there taking SG readings are doing it incorrectly anyway and using tools akin to a pitch fork for brain surgery to do so.

Depending upon how low the batts sat at dead they may or may not recover. Either way some permanent capacity will be lost but how much lost capacity is impossible to say.

monkeybars · Sep 4, 2012

1% a day is just a bit of an exaggeration doncha know

Navicula · Sep 4, 2012

Stupid question...........I gather you have shore power hooked up to your boat when you leave (120v)

jrowan · Sep 4, 2012

As others have stated your batteries are probably toast. Once they have been drawn down below 30 % repeatedly the lead plates will be damaged (assuming they're standard lead acid type). Also don't discount the problem that if you have one bad battery that it will kill the good battery, as they both will equalize their voltage if switched to all on. That's why its good to switch to one battery for engine starting & another for all house loads, which makes it more likely that one battery's voltage can be sustained & be there when you need it for engine starting. Since it is near the end of the season, you may want to wait to replace them both next spring. I would replace at least one for the winter so that you have a battey to run your pump. But many advise you to replace both of your batteries at the same time so that they will have even wear & lifespan. If you only replace one, then disconnect the other bad battery all together to stop it from killing the new one.

Jon_E · Sep 4, 2012

monkeybars said:
1% a day is just a bit of an exaggeration doncha know

Is it? That number came from Don Casey's book, "Marine Electronics Simplified", doncha know.

jrowan · Sep 6, 2012

I agree with that. Nigel Calder, the authority on all things to do with marine electrical systems states that 1 % discharge per day is normal for lead acid batteries, and actually worsens when the temperature falls dramatically. Look in his Bible of marine repair books: "The Boatowner's Mechanical & Electrical Manual." I have never found a marine repair & diagnosis guide which was more thorough or accurate. Crazy detailed when it comes to battery output, etc.

Jon_E · Sep 7, 2012

I thought I understood DC systems pretty well until I picked up Don Casey's book a few years ago. Not only does it give excellent instruction and facts, but it also goes into the why, which I think is great. This is what Don Casey's book says about self-discharge:

Wet cell plate grids are lead but alloyed with a small amount of antimony to strengthen them. The dissimilarity between the lead and antimony sets up small internal currents which allow the battery to self discharge. In warm weather an idle wet cell will lose as much as one percent of its charge per day, and more in the tropics. This means that even a fully charged wet cell will be 30 percent discharged if idle for a summer month. A battery in this state - discharged and idle - will lose capacity to sulfation.

From "Marine Electronics Simplified" - page 24

Jon_E · Sep 7, 2012

jrowan said:
... But many advise you to replace both of your batteries at the same time so that they will have even wear & lifespan. If you only replace one, then disconnect the other bad battery all together to stop it from killing the new one.

Very true. It looks like our texts on marine electronics are in total concert.

Maine Sail · Sep 7, 2012

jrowan said:
I agree with that. Nigel Calder, the authority on all things to do with marine electrical systems states that 1 % discharge per day is normal for lead acid batteries, and actually worsens when the temperature falls dramatically. Look in his Bible of marine repair books: "The Boatowner's Mechanical & Electrical Manual." I have never found a marine repair & diagnosis guide which was more thorough or accurate. Crazy detailed when it comes to battery output, etc.

While batteries can lose a lot to self discharge I've yet to see a healthy battery that loses 1% per day or 30% in a month unless it gets REALLY hot. It can happen, and the battery manufacturers spell it out, but I suspect it is on the far end of the self discharge spectrum. Being that I work on boats my barn is full of marine batteries that rotate on and off chargers so I get to see self discharge more than most.

Even in the warm summer temps I find they lose about 10% +/- per month here in Maine. Cold weather DRASTICALLY slows this process. In the cold winter months I can go three - four months on wet cells and barely drop 0.1V or 10% of capacity. The only reason I charge in the winter is to prevent stratification.

In the middle of responding to this I just went out to the barn and checked the OCV on two of my "loaner" batteries. One is a deep cycle group 31 wet cell and the other is a thin plate group 27 starting battery. The blue tape on them indicates they came off the charger on 7/12/12 and today is 9/7/12, nearly two months.

The group 31 is resting at 12.62V and the starting battery at 12.58V. The temp in my barn today is 82F but they are on the cement floor which is at 61F.. For the group 31 full is about 12.72V and for the starter about 12.69V. These batts have gone nearly two months and lost roughly 10% of capacity or about 5% per month at the average floor temp of probably 60-65F not far off from most bilge/battery compartment temps in the Northeast.. If the temps were 100F they'd have lost more and if 20F, lost less.

Can 1% per day happen, sure, but it is not what I have seen or witnessed as the norm unless the temps are pushing 100F...

I will now go swap out my batts on the charger thanks to this thread.....

jrowan · Sep 7, 2012

So there is a benefit to living in your cold climate? lol. Seriously, I believe that Calder was talking about battery loss in tropical climates. He is also wrong sometimes. In the August issue of Sail magazine he admits to giving erroneous advice telling the owner of Yanmar diesels to lock their transmissions in reverse to stop their cavitation drag. He got a lot of flack from sailors writing in to tell him that Yanmar will void your warranty if you do this. Doh! Then he tries to make a comback telling readers that they can install a seperate transmission shaft lock to prevent movement & not wreck the trans. Like anyone is really going to bother doing this. Is someone really going to run down to the rear of the engine to unlock their trans. if they need it to run the engine in an emergency? Not gonna happen. Even the experts make mistakes.

Don Guillette · Sep 12, 2012

A simple solution to the bad battery discharging it's good neigbor is to set them up so they stand alone. I had 2 house batteries and one starting battery and all stood alone. I'd start the boat and let the starting battery recharge and then switch to the #1 house on odd days and the #2 on even. The starting battery was always available to strat the boat. If I developed a problem with the starting battery, which I never did, I'd switch to "ALL" to start the boat.

Jon_E · Sep 17, 2012

kbbarton said:
... now that I most likely need new batteries, does anyone have any recommendations as far as manufacturer? I haven't found much in the way of useful reviews so far.

Don Casey (whom I greatly respect) says the best way to shop deep cycle batteries is to weigh them. The better batteries will have thicker lead plates and thus weigh more. Since I need to buy new batteries soon, I just may carry a bathroom scale with me to compare!

In the past I've had pretty good luck with CostCo brand wet cell deep-cycle marine batteries. The last pair I had had a 30 month guarantee and they lasted over 4 years. My local marine supply store's brand-name batteries cost twice as much, and though they may be better they aren't twice as good (they won't last twice as long).

jrowan · Sep 19, 2012

I ditto what Jon E said, except I've bought batteries now from Sam's made by Duracell & for the money they're pretty decent. Weight of yhe battery is likely reflective of construction build. But I will say that really big deep cell are heavy as hell & will break your back trying to get 'em on board. Make sure they have a good strap so that you & your mate can each take an end to haul on board. I generally use group 27's as the cost is reasonable, ther not excessively heavy & are affordable. I don't do too many overnights on the hook so they've worked fine for me. As far as Don G. stating switching the batteries from 1 to 2 & all, just remember not to switch the main battery switch while the engine is running, or you'll blow out the diodes on your alternator / voltage regulator!