Battery Problem?

[Tom&Shelly]

So, I turned off the shore power to our tear for a week, left just the four USB ports on, and found to my shock (or lack there-of) this afternoon, the AGM battery was down to 11.4 volts

Yikes! Didn't expect it to drain that quickly. (Naturally I put the shore power charger back on immediately.)

Odd thing is that I have a Coulomb meter on there

https://www.amazon.com/gp/product/B07CTKYFTG/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

(the one many of us have been buying lately), and it still read 100%. My thinking is that there is something wrong with the battery (at this point) and it is discharging internally, so the meter doesn't see it. That would also explain the fast discharge. Left it on a solar charger all Winter, which I thought would be okay. Maybe I'm wrong about that?

Ideas?

Edited to add More data: It's a 100 Ah battery (Group 27 AGM). The 4 USB ports, solar charger (disconnected to a panel), coloumb meter, and anything else with lights and fan turned off draws about 80 mA, for a total after the time I had shore power disconnected of 11.5 Ah. So why isn't the coloumb meter reading ~88.5%?

After a few hours of charge (shore power) the voltage is back up over 13 volts. I'll keep charging until tomorrow morning, then check the voltage after sitting for an hour.

I'll also take the cover off (not a quick job) and see if I've got water and/or debris sitting on the battery discharging it. I may try a discharge test later to see if the battery is obviously weak.

The business of the meter showing 100% vice 88.5% is what's confusing me...

Tom

[JasenC]

Are you sure you didn't get a bad meter.

[Tom&Shelly]

Are you sure you didn't get a bad meter.

It seemed to have worked correctly up to now. It's possible it went bad too, but that would be two simultaneous failures (counting a bad battery after only a year)...

Tom

[bdosborn]

Did you check the voltage reading with another meter or is the 11.4V what the AiLi meter displayed? 11.4v isn't a death sentence for an AGM, I'd charge it and still use it.
Bruce
P.S. Whenever I see a wonky voltage with the trailer or the van I always check it with a trusted meter.
P.P.S. You don't have any grounds on the upstream side of the shunt, right?

[friz]

Is it possible that neighbor kids are using it for a club house after hours? Not saying that I used to do this as a kid, bit my neighbors did have a pretty posh rig...... cool place to plan our future careers as rock stars, international spys and the such.

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[Tom&Shelly]

Is it possible that neighbor kids are using it for a club house after hours? Not saying that I used to do this as a kid, bit my neighbors did have a pretty posh rig...... cool place to plan our future careers as rock stars, international spys and the such.

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It's a good idea Friz, but very unlikely here. Area with big lots, lots of seniors (and we haven't seen any kids), and the tear is near our house.

More to the point, we're storing some blankets, towels, and such in the bed area of the tear, and nothing is moved.

Tom

[Tom&Shelly]

Did you check the voltage reading with another meter or is the 11.4V what the AiLi meter displayed? 11.4v isn't a death sentence for an AGM, I'd charge it and still use it.
Bruce
P.S. Whenever I see a wonky voltage with the trailer or the van I always check it with a trusted meter.
P.P.S. You don't have any grounds on the upstream side of the shunt, right?

Thank you for the ideas Bruce. Unfortunately, I have a choice of meters: The AiLi, the one on the Renogy solar controller, and a Harbor Fright meter in our tool box. We're at my Mom's house and my Dad's Simpson is long gone!

That said, the state I found the battery in yesterday was with the AiLi reading 11.4 volts, and the solar controller giving a low battery voltage error code. When reset, it too read 11.4 volts. Those two meters always seem to read within a tenth of a volt of each other.

I charged the battery (from shore power) overnight, turned it off this morning and, after an hour and a half, the AiLi and solar controller both read 13.1 volts without load. the Harbor Fright meter reads 13.25 volts (which is what I understand a fully charged AGM battery should read).

I opened up the battery case and all looks as expected. Some dry road dust on the battery, but no evidence of water intrusion. No evidence of mice or other animal activity. Seems unlikely there could have been some external discharge path there.

Yes, I have the AiLi sensor connected so there is no ground return to the battery that doesn't go through it.

Right now, I'm running our fan on the 2nd lowest setting, and will check the discharge rate and voltage throughout the day. I know running it that way all night left us at about 90% in the morning, so I'll see if we're getting similar performance.

Still a mystery to me why the battery discharged so much with only a week of 4 USB ports running, and why the AiLi meter didn't record the discharge (or reset if it did).

We have two weeks of mostly boondocking coming up next month, so we'd prefer a good battery. Of course, there is nothing critical that needs the power and we'll be in fairly cool climes, so we can survive without power if necessary.

Tom

[bdosborn]

Right now, I'm running our fan on the 2nd lowest setting, and will check the discharge rate and voltage throughout the day. I know running it that way all night left us at about 90% in the morning, so I'll see if we're getting similar performance.

I think that's the ticket, test it and see what happens. Your batteries are probably still covered under warranty so you could go that route if they fail your test. The Aili meter on my mini battery has never reset itself, but I don't use it very often. I was going to ask if maybe you fat fingered the buttons and reset it while you were freaking out over your low voltage but after looking at mine again I don't see how you could do that. Logic diagrams for trouble shooting my own technical issues *always* start with "Did you F with it?"
Bruce

[bdosborn]

I opened up the battery case and all looks as expected. Some dry road dust on the battery, but no evidence of water intrusion.

I just had a thought. It's a long shot but put a meter lead on the positive battery terminal and one in the dust on the battery. If there's any voltage showing then the dust could be conducting across the terminals that wouldn't show up on the Aili meter.
Bruce

[Tom&Shelly]

Right now, I'm running our fan on the 2nd lowest setting, and will check the discharge rate and voltage throughout the day. I know running it that way all night left us at about 90% in the morning, so I'll see if we're getting similar performance.

I think that's the ticket, test it and see what happens. Your batteries are probably still covered under warranty so you could go that route if they fail your test. The Aili meter on my mini battery has never reset itself, but I don't use it very often. I was going to ask if maybe you fat fingered the buttons and reset it while you were freaking out over your low voltage but after looking at mine again I don't see how you could do that. Logic diagrams for trouble shooting my own technical issues *always* start with "Did you F with it?"
Bruce

Oh ya! I agree completely! But in this case, the solar controller had a big E01 staring at me (manual says that's a low battery voltage) while the AiLi was set (as usual) to the % mode and read 100.0%

Simple, one button push to get to the voltage which read 11.44 volts. When I fiddled with the solar controller, it reset and read 11.4 volts. I did turn on the galley lights and they worked fine, and the battery voltage did not decrease.

Anyway, I ran the fan (0.22 amps) for 8 hours today, after charging overnight from shore power, and the battery voltage, beginning to end, read 12.61 from the AiLi meter, 12.6 volts from the solar controller, and a wide range of voltages from the Harbor Fright meter. I suspect its own battery is on its way out. Early in the day, it read 12.85 volts.

The AiLi meter did compute correctly, saying I had 98.2% capacity at the end of the day.

So the battery isn't terrible. I suspect, however, it isn't 100 Ah, at least not these days. That doesn't explain the AiLi reading 100% yesterday though.

So, we will take it to New England shortly, and test it over a variety of non-electrical sites, and see how it works. This may have been the first time since installing the battery that it went a whole week without charging; it was certainly the first time I had a load (0.08 amps) for a week without charging. I may try that again, keeping an eye on the meters, but not now, this close to a trip.

Tom

[Tom&Shelly]

I opened up the battery case and all looks as expected. Some dry road dust on the battery, but no evidence of water intrusion.

I just had a thought. It's a long shot but put a meter lead on the positive battery terminal and one in the dust on the battery. If there's any voltage showing then the dust could be conducting across the terminals that wouldn't show up on the Aili meter.
Bruce

Oh! wish I'd thought of that before vacuuming the dust up! My long-shot thought along those lines was it might conduct if wet, so I looked for signs of rain water, or rodent water, but didn't see either.

Tom

[friz]

I would put it through a regeneration cycle or two and see if it still meet your needs. My battery is not too healthy but I keep it going because I think the prices are still inflated on lithium. Playing the waiting game.

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[wannabefree]

There are so many factors affecting the life of a battery. I recently replaced the battery in our tear because the charger failed and let the battery self-discharge. The battery was a year old. Your battery is a year old. So check the charger. While you suggest that 2 failures at the same time are statistically improbable, that is not totally correct. A failed charger will likely take the battery with it, as I experienced.
Extreme heat and cold kills batteries. Over-discharge kills batteries. Overcharging kills batteries. Evaporation kills batteries, even AGMs. Chemical impurities kill batteries. And now that all of our batteries come from China, poor quality kills batteries.
So verify the charger is working right.
Don't put too much stock in coulomb counters. They are extremely difficult to design and really have to be tuned to the battery and charging system to be accurate. If your voltmeter and ammeter tell you one thing and the coulomb counter tells you something else, trust what the meters tell you.

[Tom&Shelly]

Just got back from two weeks camping, and now our AGM battery is displaying a classic symptom of a single dead cell. Shortly after charging, with even a modest load, it goes to about 10.5 volts. As far as I know, we haven't abused it electrically, so I'm thinking it just couldn't handle the environment of living next to the axle while Shelly was driving. (Just kidding, dear! Amend sentence to "while WE were driving")

Seriously, I think the bouncing and vibration may be what killed the battery. It was made in Vietnam and sold by Amazon, so we don't really have an effective warranty, just a good core for trade-in.

While camping, once I realized it was a single bad cell, we just went on using it, running our fan all night, charging from shore power, solar panel (not so effective in wooded sites), and from the TV when moving from site to site. Fortunately, all of our lights and fan seem to work just fine on 10.5 volts, which leads to a question--is it worth changing, or should I continue to use it until the bad cell (or aggressive driving) kills the others?

Tom

[bdosborn]

Fortunately, all of our lights and fan seem to work just fine on 10.5 volts, which leads to a question--is it worth changing, or should I continue to use it until the bad cell (or aggressive driving) kills the others?

I'd get rid of it if it was me, I'd be worried about the fan burning out from running on the low voltage.

Never underestimate Gotham City. People get mugged on their way home every day of the week. Heh, sometimes...sometimes things just go bad.

Sometimes cells just go bad...

Bruce