Battery decay

[pelikan61]

I've got a 2021 Isata 3 with ReLion RB100-LT lithium house batteries. When voltage decays, the chassis battery decays with them in parallel, volt-for-volt.

Is this normal? My assumption was that they were independent of each other. If this is by design, can someone help me understand the reasoning behind that?

The house batteries are fully charged and synchronized with the Victron. The converter and the Go-Power are set to Lithium.
Thanks

[bclemens]

How are you determining chassis battery voltage?

[pelikan61]

The only way for me to check is by the Mira control panel. They move in unison tit-for-tat to a point where a warning message is displayed on the Mercedes dash panel. I neglected to take a pic of the warning message.

[bclemens]

I would guess than that something is amiss on that connection...sounds like it is only reading the house.

[PhilFromMaine]

It shouldn't happen especially with that make and model.

There should be an intermediary device between the two batteries that prevents this. Have you independently measured the voltage at both batteries (battery banks) with a multi-meter?

[bclemens]

Originally Posted by PhilFromMaine

It shouldn't happen especially with that make and model.

There should be an intermediary device between the two batteries that prevents this. Have you independently measured the voltage at both batteries (battery banks) with a multi-meter?

There is an intermediary device to prevent this, and he mentioned that he is only getting the voltages from the screen. So I am guessing that screen is pulling only the house side.

One way to double check is the dash...turn the key on and see where the voltage sits on the chassis battery vs. what it shows on the screen. Multi-meter would be even better.

[pelikan61]

I think you may have identified something if I am understanding correctly. I just went out and turned the vehicle ON. I accessed the chassis battery info through the dash control panel.

Prior to turning it on my voltage was 13.3 volts on both the chassis and house.

After turning the engine ON, my chassis went up to 14.5 and house 14.1 volts.

Immediately after shutting the engine OFF, my voltage dropped in unison to 13.3.

Hope this has some meaning.

[pelikan61]

To clarify a bit more. When I turned the vehicle ON, the Mercedes dash and Mira indicated chassis battery 14.5.

The house battery on the Mira showed 14.1 while the engine was ON.

When I shut the engine OFF, both chassis and house indicated 13.3 on the Mira.

[bclemens]

Well part of the issue to understand is that you are not reading the battery voltage.

If you are plugged in or chassis running, you are reading the "charge voltage" NOT the battery voltage.

So when you see them both running in parallel....then you are probably seeing them being charged. Then when they stopped charging, they might fall from that 14.5 volt down to 13.3 volts pretty darn quick. That means nothing as it is just going from charging to resting.

The only way to truly know what is going on, is to be unplugged, no chassis running, no solar. See what the Mira says for house and chassis, the take a multimeter to the battery to double check.

So as of right now, I see nothing you should be worried about.

[bclemens]

PS. 13.3 is a FULLY charged lithium battery and possibly a "surface charge" on the chassis battery. A resting voltage on a fully charged AGM will be 12.8, 12.9 max.

[pelikan61]

I did as you suggested Brian, I utilized a multi meter to check the chassis battery.

And as I explained previously, the chassis battery voltage mimics the Mira display and the Victron gauge.

And now confirmed with the multi meter.

I will allow it to go down below 12volts to see if the warning message reappears on the Mercedes dash.

[bclemens]

Originally Posted by pelikan61

I did as you suggested Brian, I utilized a multi meter to check the chassis battery.

And as I explained previously, the chassis battery voltage mimics the Mira display and the Victron gauge.

And now confirmed with the multi meter.

I will allow it to go down below 12volts to see if the warning message reappears on the Mercedes dash.

Yes, but were you unplugged, with no solar? otherwise they will still read the charge voltage not battery voltage.

[pelikan61]

I am unplugged and no solar. I am currently at 11.4 volts on all three.

Mira - 11.4 volts chassis and house.
Victron - 11.4 volts.
Multi-meter - 11.4 volts.

I will let you know when the display presents the warning message.

[bclemens]

Originally Posted by pelikan61

I am unplugged and no solar. I am currently at 11.4 volts on all three.

Mira - 11.4 volts chassis and house.
Victron - 11.4 volts.
Multi-meter - 11.4 volts.

I will let you know when the display presents the warning message.

That is too low. Don't want lead acid batteries below 12v really.

Are these factory lithium or upgrade after the fact?

[pelikan61]

Factory batteries.

Well I got the message on the dash, it said to "Start Engine See Operator's Manual"

I plan on plugging it back on to shore power. I think I'm through attempting to diagnose this on my own.

The lowest numbers I have are 10.8 volts for house and 10.9 for chassis, which was confirmed by a multi-meter.

Although this is not my field of expertise, there are times when you know something isn't right and for me, this is one of them.

I got a local service center schedule me for July 6th. I will keep you advised on what they discover.

I've compiled a large amount of pics and records to help them assist.

Thanks for taking the time to assist.

steve

[Desert Boat]

If I read the RB-100LT data sheet correctly, 11.4 volts is about 2% state of charge. If your batteries are at that level, they are not getting charged, and not a place you want to be.

What voltage do you see after a complete charge cycle (five hours), with the battery charger turned off for 20 minutes or so to let battery voltage stabilize? I hope to see 13.5 or more.

Maybe there is a common point between the low SOC and pulling down the truck battery, but not coming up with it now.

In this condition, I would not be too far from a spot to plug in or jump start until it is fixed.

[pelikan61]

I really like your assessment. I think you pretty much hit the nail on the head about not being to far from being plugged in.

I believe I'm about where you indicated as far as 13.5 volts following a full charge. I get 14.5 volts at fully charged, then I believe I hover in the range you specified.

I spent at the least 2 1/2 hours on the phone with ReLion and compiled 15 hours of data for them. After they analyzed the information, they confirmed the batteries are functioning normally.

My concern now is, as the house battery voltage decays the chassis mimics the decay. Unfortunately, there has not been a viable solution as of yet. Like I mentioned previously, everything I look at in the RV, i.e. gauges (Victron, Mira, Go-Power) they all coincide. And now, utilizing a multi-meter the chassis battery reading matches the Mira every step of the way.

I do heed your advice not to be too far off grid until I get this addressed.

Thanks

[Desert Boat]

Thinking more about it, sounds like your BIM is stuck in the engaged position, or maybe wired wrong, or something wrong with cross connect switch. I do not know where the cross-connect button is on the 3s, but that might be a starting point. And maybe post a picture of the BIM wiring to see if anyone can spot something suspicious.

(At least i presume the 3s must have a BIM to separate the batteries.)

Were you boon docking when you saw the 11.4 on the house batteries?

[FollowTheSun]

Originally Posted by pelikan61

I've got a 2021 Isata 3 with ReLion RB100-LT lithium house batteries. When voltage decays, the chassis battery decays with them in parallel, volt-for-volt.

Is this normal? My assumption was that they were independent of each other. If this is by design, can someone help me understand the reasoning behind that?

The house batteries are fully charged and synchronized with the Victron. The converter and the Go-Power are set to Lithium.
Thanks

Mercedes requires the RV manufacture to isolate their battery from the coach battery except for charging. That is, when the Sprinter's motor is not running its battery must disconnect from the coach battery. However, when the motor is running, then the two battery systems may be connected together so that both charge. This connect/disconnect should be accomplished automatically by an isolation relay, usually installed near the Sprinter's battery (under driver's floor board). Based on your various descriptions, it sounds as though that isolation relay is defective (always stuck on), effectively connecting the two battery systems together all of the time. This would explain why the voltages on the two system always track each other. Since your Isata 3 is 2021, this matter should be covered by your RV warranty.

[pelikan61]

That makes a whole lot of sense. Appointment is on the 6th off July, is it something easily swapped? If so, I’ll do it myself.
Thanks for the info.