Marine battery acting strangely

Desert Rat · October 2017

I have a new 12V deep cycle marine battery in my camper trailer. When charging, it immediately (within a few seconds) goes to 15.0-15.1 volts. This is happening with three different charging sources: the converter in the trailer, the 100 watt solar panel & Morningstar Sunsaver charge controller in the trailer, and my automotive battery charger. The thing is, the battery passes a load test with flying colors. I had a similar situation a couple of years ago with an Optima battery in one of my trucks. The battery was showing 17 volts while charging. After replacing two alternators, I finally realized it was the battery itself. What causes a battery to do this?

Estragon · October 2017

A fully charged battery will get up in voltage pretty fast. 15.1 is a bit high for an absorb voltage though. Do you know what the sunsaver is set to for absorb voltage If temperature compensated, charging voltage could be in that range if cool/cold.

mike95490 · October 2017

first guess would be a sulfated battery. but you say it passes your load test. ??

Desert Rat · October 2017

Absorption voltage for the Sunsaver is 14.4V. It does have temperature compensation via a sensor on the controller itself, not a remote sensor. Ambient temperature today was around 75⁰ F.

Estragon · October 2017

At 75°f, the controller should be keeping voltage at pretty close to 14.4v. Dunno. Where/how are you measuring 15.1v?

Desert Rat · October 2017

Estragon said:

At 75°f, the controller should be keeping voltage at pretty close to 14.4v. Dunno. Where/how are you measuring 15.1v?

I have a digital voltmeter connected to the load terminals of the Sunsaver. I did that in order to be able to shut off the display (as well as the blinking lights on the Sunsaver) at night since they are next to the bed in the trailer. I have confirmed the same voltage with my multimeter directly at the battery terminals.
I checked this morning, and the voltage has already hit 15V less than an hour after sunrise. This is with a 100 watt panel that is mounted flat on top of the trailer. Sure seems like a defective battery to me. Are there any other tests I can do to confirm?

706jim · October 2017

In my experience, a battery that reaches a high voltage with a limited amount of amps input is toast.

Estragon · October 2017

When you say "the battery passes a load test with flying colors", how did you test? Was it a short test done with an automotive type tester, or an extended test with a smallish known load?

Is the battery flooded, or VRLA (sealed)?

Desert Rat · October 2017

Estragon said:

When you say "the battery passes a load test with flying colors", how did you test? Was it a short test done with an automotive type tester, or an extended test with a smallish known load?

Is the battery flooded, or VRLA (sealed)?

Automotive load tester.
Flooded.

Estragon · October 2017

I would do 2 tests then:

1. Test specific gravity on each cell with a hydrometer, and make sure electrolyte is covering plates in all cells. Add distilled water if needed. SG should be ~1.26 -1.29 in all cells, and within 0.02 between cells.

2. Test capacity by attaching a load like incandescent lighting with a known draw of around 5-10% of battery capacity. Time how long it takes to get the voltage down to ~11.5v, then recharge, noting time it takes to get to ~14.4v. During this test, monitor battery temperature regularly, ideally with a laser type meter, but just your hand will do. It should never get more than mildly warm (~85-90°f). If it gets hot (> about 100), especially if voltage is changing quickly, STOP the test, as the battery is a goner and further testing could be dangerous.

Desert Rat · November 2017

I've been away for a few days; back on it now.
I tested SG and got these readings:
1.235
1.235
1.235
1.245
1.240
1.225
Do you think that's too big a spread?
I'm now running a vent fan in the camper and monitoring voltage.

BB. · November 2017

In times past, I believe it was Trojan, was calling for equalization when SG varied by 0.015 or 0.030 between high and low cells.

The reality is--Equalize until SG no longer rises (20-60 minutes between readings). Once it stops rising in all cells, then that is the new 100% full reading. Log SG and temperature (temperature corrected SG) and go on from there.

With some of the Rolls/Surrette batteries, deep cycling and EQing has shown to bring up "weak cells" over time. But doing this with a marine battery (which tend to have thinner plates), may be hard on the battery itself (just EQing is hard on batteries).

In warmer conditions (tropics), and for long life applications, lower "full" SG values can be helpful for a longer battery life.

Of course, SG meter technique matters too... Gas bubbles on float, temperature, dirty/sticky float, hard to read scales closer than ~0.002 units of precision, etc.

-Bill

From and older set of posts:

BB. said:

Re: Confused with % of Battery discharge

A 48 Volt Bank at resting voltage at 77F is around 45% state of charge (see generic bank voltage chart from Battery FAQ--12.00 volts).

However, the actual resting voltage is really dependent on the initial specific gravity of the electrolyte fill...

So, what was your "full charge" Specific Gravity?

One thread here
Another thread here

So, to pull from earlier posts:

Well mixed electrolyte is important--so if you notice all cells not coming back to "full charge" level of s.g., then there is a good chance that "mixing" (equalization) will bring the s.g. back up to your logged readings (keep these as your "good batteries" / "fully equalized" numbers.

The amount of variation you are seeing is not that great (less than 0.030 between all cells). And having "high" s.g. is not always a good thing either.

I ran across this page on why different types of batteries have different starting s.g. fills... Is pretty interesting:

Specific Gravity vs Applications
1.285 Heavily cycled batteries such as for forklifts (traction).
1.260 Automotive (SLI)
1.250 UPS – Standby with high momentary discharge current requirement.
1.215 General applications such as power utility and telephone.

As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

...

Higher Gravity = vs Lower Gravity =
More capacity / Less capacity
Shorter life / Longer life
Higher momentary discharge rates / Lower momentary discharge rates
Less adaptable to "floating: operation / More adaptable to "floating" operation
More standing loss / Less standing loss

Also on that page is the formula between cell resting voltage and specific gravity:

Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
Or
Single-cell open circuit voltage = specific gravity + 0.845.

So, if you are getting 46 volts after resting, if the formula is correct (and your battery is around 77F) your specific gravity should be:
46v/24cells - 0.845 = 1.072 (dead?)
47v/24cells - 0.845 = 1.113 (~20% state of charge)
Yuasa states that the temperature correction for SG is:
specific gravity changes by +.001 for every -3 degrees Fahrenheit.
J.R. Buchanan did a nice set of charts on battery SG and temperature based on a 100% charge = 1.265 SG.

By the way, do you have a Battery Monitor?

-Bill

Estragon · November 2017

Like @BB said, the range is maybe a bit wider than you'd ideally like, but in the ballpark of normal. When they stop rising, the batteries are about as full as they ever will be. Load testing will tell you if the capacity remaining is worth it to you to keep them in service.

Remember to keep an eye on temp as well as voltage.

Photowhit · November 2017

BB. said:

...Equalize until SG no longer rises (20-60 minutes between readings). Once it stops rising in all cells, then that is the new 100% full reading. Log SG and temperature (temperature corrected SG) and go on from there.

I think the normal procedure is to equalize checking the specific gravity each hour, when you have 2 hours with out an increase in specific gravity, then consider that the new 'full'...

It sounds like from your SG readings your batteries are less than fully charged, typical SG readings correspond to rough State of Charge;

Image: http://modernsurvivalblog.com/wp-content/uploads/2013/06/battery-state-of-charge.jpg

You would want to fully charge your batteries before starting equalizing.

I would almost say that your meter is wrong on the voltage, but I can't imaging 2 being wrong, though it happens. Voltage is a poor indicator of State of Charge, particularly in an active system. ...but voltage above 15 volts daily will create issues, have you needed to add a lot of distilled water? Above 15 volts your battery should be outgassing a good bit.

When you load tested you used an automotive load tester and applied a 100 amps load for 10 seconds, What did the voltage drop to and did it return to above 12 volts right away?

Desert Rat · November 2017

Photowhit said:

When you load tested you used an automotive load tester and applied a 100 amps load for 10 seconds, What did the voltage drop to and did it return to above 12 volts right away?

During the load test the voltage dropped to ~11.2V, and returned to 12+V right away.

Yesterday I turned on a vent fan in the trailer which draws 1.25A. The starting battery voltage was 12.6V. After 8 hours of running the fan the voltage was at 12.3V. (No solar charging during this test)
This morning I connected the trailer converter to AC power, and the battery voltage immediately went to 16.4V! I also tried an automotive battery charger, and the voltage went to 15.5V. So that's three different charging sources that have sent the battery voltage to 15+ volts. And these voltage readings were confirmed by 4 different voltmeters.
All talk about SG aside, it looks to me like this is a defective battery. It is less than one month old; I'm going to return it.

706jim · November 2017

I purchased a boat equipped with two group 27 Interstate batteries. One year later, I replaced both of them with group 31's. These have lasted 10 seasons now. The original group 27's would simply not hold a charge.
As one GM electric car designer stated: "There are liars, damned liars and battery suppliers!"
One month old or not, I think you have a lemon.

Desert Rat · November 2017

One of my favorite sayings is:
Most batteries don't die of natural causes; they are murdered.
I believe this is one that died of natural causes at a very young age!

Marine battery acting strangely

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