What's Going On With These Batteries?

[CapnCrunch]

My batteries don't seem to be charging fully lately and, when looking at them, I noticed that several had slightly corroded connections. I decided to clean all the terminals and do a little testing while I was at it. Before doing any of that, I shut off all DC appliances, etc.

My process was to shut off the chargers (solar and AC), isolate all 5 batteries, clean all cables and posts, check voltage on each battery, then reconnect them all and again check the voltage on each. Here's what I got. (voltages are isolated/connected)

Battery A - 12.84/12.72
B - 12.87/12.68
C - 12.84/12.92
D - 12.82/12.89
E - 12.87/12.90

To make matters more confusing, my BMV 702 reads 12.63 after all the cleaning. Is this odd or am I nit-picking?

[GrowleyMonster]

Originally Posted by CapnCrunch

My batteries don't seem to be charging fully lately and, when looking at them, I noticed that several had slightly corroded connections. I decided to clean all the terminals and do a little testing while I was at it. Before doing any of that, I shut off all DC appliances, etc.

My process was to shut off the chargers (solar and AC), isolate all 5 batteries, clean all cables and posts, check voltage on each battery, then reconnect them all and again check the voltage on each. Here's what I got. (voltages are isolated/connected)

Battery A - 12.84/12.72
B - 12.87/12.68
C - 12.84/12.92
D - 12.82/12.89
E - 12.87/12.90

To make matters more confusing, my BMV 702 reads 12.63 after all the cleaning. Is this odd or am I nit-picking?

FLA batteries? Checked the water lately? How old? Try an equalizing charge. Could have something to do with the length of the electrical path from charger to each individual battery. If you have a copy of Nigel Calder's excellent book it is worth a read. I don't have mine with me of course.



I assume all 5 are in parallel. Maybe split them into two banks for now, the first two together and the last three together. But I bet they are overdue for an equalization.

[GrowleyMonster]

Oh, and how old are they? Maybe after a few charge cycles, with nice clean and tight connections, the first two will perk back up a bit.


And am I missing something? I am assuming that the first number is voltage while connected in parallel and the second number is isolated but on re reading, you seem to state that it is the other way around. In parallel they most certainly should read the same voltage, with clean connections. Isolated, they can very well be slightly different. The amount different in this case is kind of a big deal.

[CapnCrunch]

Originally Posted by GrowleyMonster

Oh, and how old are they? Maybe after a few charge cycles, with nice clean and tight connections, the first two will perk back up a bit.


And am I missing something? I am assuming that the first number is voltage while connected in parallel and the second number is isolated but on re reading, you seem to state that it is the other way around. In parallel they most certainly should read the same voltage, with clean connections. Isolated, they can very well be slightly different. The amount different in this case is kind of a big deal.

Yes, they are in parallel. And, yes, the first number is the isolated value. Thats kind of what got me scratching my head, too. I'm beginning to wonder if my multimeter hasnt gone haywire. I should have mentioned that the water levels were fine in all battys and battys B thru E were all new in 2016.

[a64pilot]

A couple of things, first it’s likely they are sulphated to some extent, and secondly, just because a digital product reads to two or three decimals, does not mean it’s accurate or repeatable.
Then technique does matter, making sure your leads are clean and fully inserted and that you press and move the probes around until the highest reading is obtained.
That is why I bite my tongue with these threads saying a $10 multimeter is as good as a Fluke, it’s possible, but unlikely. Even my Fluke when I used it for measurements that we turned into the FAA for certification, had to be calibrated to NIST standards within the preceding 90 days.
I don’t know how you calibrate one, I assume it’s really an accuracy check, not sure if anything can actually be adjusted like you do for torque wrenches for example.

I’m saying all this without knowing what multimeter you have, so I may be fixing to be embarrassed.

[CapnCrunch]

Originally Posted by a64pilot

I’m saying all this without knowing what multimeter you have, so I may be fixing to be embarrassed.

LOL I dont think youre going to be embarrassed today My meter is a TEK that cost @$35, if I recall correctly (which, at my age, is highly unlikely). Anyway, I did notice fluctuations between multiple readings of the same battery but wasnt sure how to interpret the fact that there were differences. I was wondering how I could get different values at individual batteries connected in parallel.

I'm still learning the nuances of batteries and charging systems and, thus, will ask several rookie questions. Y'all have been a great source of info, so far, even though you guys often cause my eyes to roll back in my head in confusion LOL.

So, if I'm reading this right so far, it looks like I have at least one weak battery and a sketchy multimeter.

[Locquatious]

Check the temperature of the batteries. If one is warmer than that others it is going bad and, like a drowning man being saved, will pull down the other batteries till they also fail.
Also, my Fluke leads are often to blame when making measurements. Usually it is the alligator to point probe connection. The screw-on type are better but even they have corrosion/contact issues.

[roland stockham]

I agree with A64 pilot. Unless you are reading in lab conditions with a calibrated professional meter I would ignore the second decimal place on the meter. Also a difference of 1/100 of a volt is meaningless when it comes to batteries. The voltages on batteries A & B showing differences in 1/10v. This suggests they are supplying some current either to the system or the other batteries so there is some imbalance. As others say check electrolyte and try an equalization charge (if you batteries can take it) and see if it goes away. Try also multiple charges (fully charge, knock the voltage down with something like the inverter or windlass, repeat for 10-12 cycles over a couple of days) this ensures batteries really are at 100% charge. If the imbalance remain it is likely a battery age effect. Battery age is not measured in years, there lifespan is mostly dependent on quality and maintenance. Top grade FLA's can last 10yrs+ if properly looked after. Cheap so called deep cycle FLA's aimed at the RV market generally seam to do 2-3yrs but can easily be trashed in a season.
Give details of you batter make/model, age, normal cycle depth and charger setup and people can comment further

[a64pilot]

As with anything there are manufacturing tolerances too, it’s not likely that all batteries that roll off of an assembly line are identical.
I’d bet if you complained to who sold you a battery that it was .1V lower than the other, they would likely think your a nut.

[hamburking]

try a fresh/new battery in your voltmeter before you go any further.

[GrowleyMonster]

JUST TO BE ABSOLUTELY SURE, since it is impossible for parallel batteries to show different voltages in a simple bank with decent connections...


Try completely disconnecting the batteries and test each one. Thats right... take off all terminal connections so they are as naked as they day you bought them.


Now...



connect them all in parallel with new wire, any size of at least say 4awg, with new lugs, after scrubbing terminal posts with a wire brush. Do not connect the bank to ANYTHING. Take your voltages. They will, of course, all read exactly precisely the same.


Now connect the bank to your DC electrical system.


I think possibly what is going on is your connections are still not very good. Probably where #2 is connected to #3. Your system is drawing from the bank nearer the #1 battery. With any load at all, even a partial short to ground, the voltage in the first two batteries is pulled down while the last three, not so much.



If your subsequent testing indicates this sort of problem, simply rewire the whole mess with nice new cable and high quality lugs.

[pcmm]

My first guess (based on the readings) is that the main pos and Neg for the whole bank are connected to the first battery in the string.

[GrowleyMonster]

Originally Posted by pcmm

My first guess (based on the readings) is that the main pos and Neg for the whole bank are connected to the first battery in the string.

Exactly. And anything but the very best connections between the batteries will draw down the first battery or batteries before the others further from the system connection. The use of small cable could also cause this effect, or longish runs between batteries. IOW, more than a few inches.


BTW Crunchie, another interesting experiment would be to move the system connection down to the other end of the bank and see if your voltage discrepencies swap ends, too.

[CapnCrunch]

Update, etc.:

I should maybe have specified that the voltage values I initially gave were taken as each battery was first disconnected from the bank and then, again, when all the batterys were reconnected. I checked them again this morning and all read around 12.84. It looks like maybe I just didnt give them time to equalize after re-connecting. (BTW: pcmm was right. The bank is connected to the panel at battery A However, I had turned everything off, so i dont know where any drain could have come from)

The next thing I dont understand is why my BMV 702 shows 11.9v when the bank reads 12.84 with the multimeter, unless the difference is caused by my fridge (which draws about 5.5A, according to the BMV).

[ramblinrod]

Originally Posted by CapnCrunch

My batteries don't seem to be charging fully lately and, when looking at them, I noticed that several had slightly corroded connections. I decided to clean all the terminals and do a little testing while I was at it. Before doing any of that, I shut off all DC appliances, etc.

My process was to shut off the chargers (solar and AC), isolate all 5 batteries, clean all cables and posts, check voltage on each battery, then reconnect them all and again check the voltage on each. Here's what I got. (voltages are isolated/connected)

Battery A - 12.84/12.72
B - 12.87/12.68
C - 12.84/12.92
D - 12.82/12.89
E - 12.87/12.90

To make matters more confusing, my BMV 702 reads 12.63 after all the cleaning. Is this odd or am I nit-picking?

So when connected in parallel you are raading 12.84 +/- .03 Vdc that could
Be she difference in probe contact resistance or RF through you body and variable proximity between your fingers and the probes. On the isolated side,this could be the difference in battery performance, and those favoured /disfavoured by cable resistance to charger.