Battery states of charge

[Ken Pole]

I have three Odyssey PC680 AGM, two of which I run in parallel as a house bank and the other as a starter battery. I should note that my cranking needs are relatively small (a thoroughly rebuilt Atomic 4 in my C&C 27) and with all-LED lighting my house needs are minimal. I have two 100W panels on my bimini which put out 7A through an MPPT controller.

That said, I managed to draw down all three to approximately 4.9V when I left my battery switch on All when I was away from the boat for a while. As soon as I discovered the problem in November shortly after the boat put on the hard for six months (Ontario), I thought they were toast. Even so, I zapped them all (at home) with the Schauer ChargeMaster recommended by my battery retailer. It charges them at 13.5V

They currently show 12.59, 12.97 and 12.96 and my retailer (who'd obviously like to sell me new ones) says thy should be fine. He suggested, however, that I pair the two higher-voltage batteries as my house bank and use the other for starting.

Any thoughts would be appreciated. Thanks in advance.

[smac999]

How long did they sit for at 4V? The sitting is much worse then the draining. Ie more then a day is bad. Weeks. Months?

You need to fully charge each one. (With a 14.4v charger). And then do a controlled 20h discharge test on each separately.

This will probably help them too if they are still ok.

[ranger58sb]

From Odyssey manuals:

12.84V is fully charged. Bulk/absorption charge should be between 14.1-14.7V, they say with a minimum of 40A. Float charge should be between 13.5/13.8V.

Suggested charge time for a 100% discharged (11.5V) PC680 is 2½ hours on a 10A charger, and 1¼ hours on a 20A charger.

-Chris

[john61ct]

There is no hard and fast line between "damaged" and wow you lost a lot of cycles off their lifetime.

A 20-hour load test is really the only way to know.

But if your usage pattern means you can tolerate risk of failure, always close to someplace new replacements can be bought, have backup for emergency cranking,

then maybe you can afford to push the envelope.

FFR a hard LVD cutoff at 10-11V will prevent that from happening.

[a64pilot]

Originally Posted by ranger42c

Suggested charge time for a 100% discharged (11.5V) PC680 is 2½ hours on a 10A charger, and 1¼ hours on a 20A charger.

-Chris

These must be some really truly magical batteries then to go from zero to full charged in 1 hour and 15 min.

Must be awfully small batteries to, cause a 20 amp charger even if acceptance stays above 20 amps and never drops to completely fully charged can only deliver 25 AH in one hour and fifteen minutes, and that is assuming 100% efficiency.

Seeing as how that stat is obviously nonsense, it makes one wonder if any of the other numbers are even close?

Not beating on you, I know your quoting manufacturers stats, just pointing out the manufacturer is either full of it, or I really don’t understand batteries.

[ranger58sb]

Yep. According to the Odyssey chart, PC680s are 170 CCA, 280 MCA, and 16-Ah capacity at the 20 hour rate. Way small.

https://www.odysseybattery.com/Specs/ExtremeSeries

-Chris

[Ken Pole]

Thankyou one and all. Going to try the 20-hour load test. And, yes, the batteries are small; I can lift them with one hand, which facilitates taking them home each winter. The A-4, for those of you unfamiliar with it, is a four-cylinder gasoline engine with total displacement of one litre so the cranking requirements are minimal. I can easily crank it by hand if necessary and have done so a couple of times just for the experience. My alternator and the solar panels generally keep the topped up with no problem until I caused this latest issue.

[john61ct]

Perfectly suitable for light cranking duty.

Need a lot more than 40Ah to act as a House bank in most scenarios, in lead those units should require a strapping young human to carry them around.

Too many in parallel also NG, better to go to 2V cells for that purpose if needed.

And even though small, for good longevity will need at least several hours to get back to 100% Full, that standard needs an ammeter to measure trailing amps.

[john61ct]

Originally Posted by Ken Pole

My alternator and the solar panels generally keep the topped up with no problem until I caused this latest issue.

You would likely not know this without verifying with an ammeter.

Even the most expensive and fancy charge sources are not to be trusted, especially if left at their default settings.

[senormechanico]

Originally Posted by smac999

How long did they sit for at 4V? The sitting is much worse then the draining. Ie more then a day is bad. Weeks. Months?

You need to fully charge each one. (With a 14.4v charger). And then do a controlled 20h discharge test on each separately.

This will probably help them too if they are still ok.

A couple of years ago, we left our house for six weeks on the boat.
Both car batteries were flat when we came home, the onboard computers supposedly drained them.
One car's battery was at 2+ volts, and I was convinced it was toast.
I charged it up overnight to14.4 and it's still running fine today.

[john61ct]

Sure, could lose a very large percentage of cycle lifetime off the back end, and still get many years of service out of a good battery otherwise well treated.

[roland stockham]

Rather than full cycle I have found that cycling repeatedly between 100% and about 80% for a few days can help batteries recover. I do it by putting a high load on the battery via the inverter for an hour then switching it off and putting the charger back on. Do this for 2 or 3 days and you may see capacity improve. Not sure of the science but I think it helps remove any sulfate deposits that have not yet fully hardened. Always been told never to fully discharge L/A batteries unless you have to even for testing.

[George DuBose]

BatteryMinder makes pulsating chargers that are supposed to desulfate AGM batteries. I have been using one for 5 years and three of my Optimas were flat for several months in the winter of 2006.

These batteries are still working 13 years after I bought them.

I am saving up for some Firefly batteries.

[sv whiteout]

They are motorcycle batteries. I use one in my BMW K75RS. I have an A4 also. My house bank is 2 Deka Group 31 gels.

They may work fine. Let us know if they seem to have lost any capacity when it warms up and you get to use the boat again.

john

[Ken Pole]

Launch isn't until 04 May (we still have more than a metre of ice in our harbour) but I will post results. Again, thanks to all for the feedback.