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Old 08-22-2022, 02:15 PM   #1
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Exclamation New AGM house battery not holding charge

Hi all! I'm new to the forum, so apologies if this or something similar has already been covered elsewhere.

I have a 2011 MB 2500 Sportsmobile that I bought last fall. The battery was ~3 years old at that point, but has worked well since then. (The inverter has always drawn it down very quickly, so I usually run the engine if I need the inverter on for extended periods of time, but otherwise no battery issues.)

Maybe a month or so ago, I noticed that the battery no longer seemed to be charging off of the solar panels. When I plugged the van in, it also didn't charge. When I turned the engine on, the battery reading on the solar charge controller immediately jumped to "fully charged" (not the usual behavior) but drained as soon as I turned the engine off.

I figured the battery had finally died, so I just had a new 12V AGM battery installed. Unfortunately, I'm still seeing similar issues. If the van is in direct sunlight, it sometimes says it's charging, though the battery still reads low. (The van is usually parked in front of my house with ample sunlight, and it'll only say it's charging when the sun is directly overhead.) It's still not charging when plugged in, and it's jumping to fully charged/draining quickly off of the engine. With only the fridge running, it reads extremely low by the next morning and has once or twice shut the fridge completely off due to low battery.

The previous owner had mentioned to me that he had to replace a fuse on the chassis battery a couple times when the house battery stopped charging while the engine was on. I pulled that fuse out and replaced it, but that doesn't seem to have helped at all. (It didn't look blown, but I had extras, so I figured I'd give that a try.) When I reached out to him, he said he had never experienced the issue I'm having now and suggested I reach out here.

I'm at a loss for what to try next or if I just need to take it in and have someone look at it. If anyone has any suggestions or has had a similar experience, I'd appreciate your feedback! I'm located in the Denver area, so any recommendations on who may be able to help locally would be great. Thanks!!
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Old 08-22-2022, 02:34 PM   #2
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Have you checked the reset switch on the inverter? And do you turn the inverter off while not needing 110 voltage?
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Old 08-22-2022, 02:39 PM   #3
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Welcome.

If I understand correctly, the new battery is exhibiting the same behavior after being charged with solar, van alternator, and plugged in/while charging via charger?

Have you checked the voltage of your charging sources?

Have you checked the new battery with a multimeter? Did you have a shop install the battery?

It is possible the new battery is dead. Not unheard of. Should be under warranty?
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Old 08-22-2022, 02:50 PM   #4
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Thank you both for your responses!

@twoxentrix I haven't reset the inverter - I can try that, but I always leave the inverter off unless actively using it. (I only need it on for the microwave and hot water, both of which I don't use very often.)

@marret yes, that's correct. The new battery seems to be holding slightly more charge than the old one (it at least occasionally seems to be charging off the solar panels and gets a little bit of charge from the engine), but it still drains as soon as it stops charging off of either of those. It was doing the same thing prior to replacing the battery. I did have a shop install the battery, and I took it back to them when I was still having issues. They checked the battery and told me the battery itself was fine, but they weren't able to diagnose what else was going on. (They're an autobody shop and don't have experience with solar panels or the other electrical work in the van, so they were limited to just inspecting the new battery.) I'll try to check voltage of charging sources and see what I find there.
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Old 08-22-2022, 03:10 PM   #5
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I would want to confirm the battery is good and your charging methods are actually working.

Do you have a battery monitor?

Checked all your cable connections? Make sure they are clean and tight, especially at the battery. Any signs of corrosion?

Hopefully Scalf77 will be by, our resident electrical expert.
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Old 08-22-2022, 03:28 PM   #6
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Thanks, @marret. I don't have a battery monitor but will see if I can track one down, and I'll double check all of the battery connections. Appreciate your help!
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Old 08-22-2022, 03:51 PM   #7
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Welcome.

Harder for us to help when we don’t know voltages. Having and learning to use a multimeter is extremely helpful. I had a similar situation that turned out to be loose connections.

There are different battery monitors from simple volts display to state of charge, amps in/out, etc.

What brand solar controller and inverter/charger do you have?
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Old 08-22-2022, 04:59 PM   #8
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Generally it would be good to list your equipment.

Sounds like you have a inverter so I assume Inverter/charger?

You have a solar charge so what controller, do you happen to know the panel or panels size (wattage).

I would assume that you have a Blue Sea ACR, for alternator to House battery charging.

Being that you it appears none of your charging paths appear to work, it should be a main path to the battery or a ground connection. All the connection are areas that are of concern, a majority of issues start with improperly torqued connections.

The picture below is the ending result of a loose connection, the nut for the fuse holder was actually melted into the plastic cover of the fuse holder. Loose connections cause arcing and high resistance in your connections.



-greg
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Old 08-22-2022, 09:46 PM   #9
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You need to check the voltage at the battery terminals while charging to make sure its reaching at least 14.4 volts (some agm's require even higher voltage 14.7 volts to fully charge, check what your brand battery recommends). Check the voltage directly at the terminals with a multimeter so you get the most accurate reading.

What you describe sounds like an undercharge battery.
I used about 4 different solar charge controller PWM and MPPT, and all of them were undercharging my batteries, they were never reaching 14.4 volts due to voltage drop and just bad calibration. If your controller goes into float mode very quickly, thats a sign you have voltage drop. The controller thinks the battery is full and reduces the amps going to the battery.
Charging with the alternator wont help much since it will only charge the battery to about 80 percent than it reduces the amps, it takes many hours of driving to fully charge.
What size solar panel do you have? and what is the max amps you see going into the battery during full sunlight?

Its likely the battery is not fully charging to 100 percent everyday, and your using more power than is being replaced. Little by little it will drain the battery.
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Old 08-22-2022, 11:03 PM   #10
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Sounds like other issues in your case but making sure your solar panels are completely clean would be worth adding to the to-do list.

I will be back at Colorado Camper Van in Loveland next week if you have not resolved and want to have another set of eyes look it over.
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