Dead Battery on Mercedes Isata 3

[caswelld]

For the 3rd time now the chassis battery is dead after sitting for just 2 weeks. Nothing is plugged into the DC outlet. I don't see any parasitic drain on the system. I'm glad the house batteries were available!

I mentioned this to the tech at the dealer and he said MB has had a lot of issues with this. He said they start the MBs on their lot every week.

Any known fix, or is it off to Mercedes?



Dave

[bclemens]

When it was sitting, were the jacks down?

We had a very weird case where an AGM battery had a dead short in the battery. The battery guy said is was likely overcharged and a cell burst??? or something. That jacks then became a ground and it would drain the chassis batteries within days.

THAT ONE took an eternity to solve. The issues was intermittent.

[bratbros]

Originally Posted by caswelld

For the 3rd time now the chassis battery is dead after sitting for just 2 weeks. Nothing is plugged into the DC outlet. I don't see any parasitic drain on the system. I'm glad the house batteries were available!

I mentioned this to the tech at the dealer and he said MB has had a lot of issues with this. He said they start the MBs on their lot every week.

Any known fix, or is it off to Mercedes?



Dave

I had a Thor Siesta for a short period of time....wasn't happy with it for a LOT of reasons...but one of them was this issue. Mercedes said it was a problem with the coach and the motorhome dealer said it was a problem with the Mercedes chassis. Never got it solved before I traded it off. It didn't matter if I disconnected the battery even...weird.

Sorry I don't have an answer for you.

[caswelld]

Originally Posted by bclemens

When it was sitting, were the jacks down?

We had a very weird case where an AGM battery had a dead short in the battery. The battery guy said is was likely overcharged and a cell burst??? or something. That jacks then became a ground and it would drain the chassis batteries within days.

THAT ONE took an eternity to solve. The issues was intermittent.

Negative on the jacks. I read on IRV2 that this is a problem with lots of MBs. It was recommended to pull the battery disconnect near the accelerator pedal if your not going to drive it for a couple of weeks.

[bclemens]

I do know a lot of the new vehicles have tons of electronics. The Ram has two chassis batteries.

[bratbros]

Originally Posted by caswelld

Negative on the jacks. I read on IRV2 that this is a problem with lots of MBs. It was recommended to pull the battery disconnect near the accelerator pedal if your not going to drive it for a couple of weeks.

The Siesta that I had (MB chassis) would even go dead if you used the battery disconnect near the accelerator. The down side to using that disconnect is that, on this one anyway, it would mess with the emissions system and every time you would reconnect the battery the check engine light would come on and you would have to reset the computer. Also, all of the clocks and radio presets, etc. would be gone and would have to be reset. Right before I got rid of it Thor told me there was a relay of some sort on the coach that could go out and could be the cause of the battery drain. Might be something to explore.

[Gordonws]

I have a Coachmen with a Mercedes also. I had the same problem then discovered a red connection next to the gas pedal. You pull that apart and it stops everything from going to the battery. Works great...no more dead battery.

[FFred]

"It didn't matter if I disconnected the battery even...weird."


If the battery dies when disconnected its a BATTERY problem.

[KatanaPilot]

Originally Posted by caswelld

Negative on the jacks. I read on IRV2 that this is a problem with lots of MBs. It was recommended to pull the battery disconnect near the accelerator pedal if your not going to drive it for a couple of weeks.

Assuming the Isata 3 is wired similarly to the MBS Foresters and Soleras, pulling the ground disconnect will have no effect. Why? Because the coach wiring to the chassis battery provides an alternate ground path. Quick way to check - pull the disconnect, open the coach door. Does the instrument panel light up? If so, the chassis battery is providing power to the chassis.

If you remove the cover on the chassis battery, you will see the additional cables installed at the factory which provide power and ground. I expect these cables are what supply charging current to the coach batteries when the chassis alternator is running. I think the Isata has a boost switch so power also has to flow from the coach to the chassis batteries too.

[bratbros]

Originally Posted by FFred

"It didn't matter if I disconnected the battery even...weird."


If the battery dies when disconnected its a BATTERY problem.

That's exactly what I thought. However, the motorhome dealer said it was good. Took the coach to and independent battery store...they said it was good. Took the coach to Mercedes...they said it was good, and by the way, since the dealer had replaced the original battery at some point I had to pay Mercedes $250 to get the motorhome back. They wouldn't cover anything under warranty since it wasn't a Mercedes branded battery. I eventually got the motorhome dealership to reimburse that....

[caswelld]

Well, I pulled the battery disconnect at the accelerator and saw an "Important" sticker. It said to allow 10 minutes after engine shut down for the emission control system to do its thing before pulling the disconnect. I guess this is a common thing to do in MB world.

I'll find out in a few weeks it worked.

Brian, just wondering if your guys pull that cable on all your MB chassis while they're waiting to enter production? How long do the MB chassis typically set around before production?


Dave

[Bill Davis]

I’ve had mine for a year and a half and have not had this issue. I don’t plug it in, The solar keeps all the battery’s happy. I don’t use the disconnect either.

[caswelld]

Yup...if you store your motorhome out in the elements with solar it will keep ahead of all the parasitic electrical draw MB designed into the chassis.

But we store ours in a garage, so it looks like I need a battery disconnect.

[JLeising]

Originally Posted by Bill Davis

I’ve had mine for a year and a half and have not had this issue. I don’t plug it in, The solar keeps all the battery’s happy. I don’t use the disconnect either.

Similar on our 2012 MBS. Not sure what may have changed on the MBS side since 2012, but no such problem on ours.

My thought- pull a battery cable off the chassis battery and put an amp meter between the battery terminal and the cable. Pulling the cable off the battery terminal eliminates any question wrt an alternative ground through the coach, or related. If significant current flowing, I would first start disconnecting any wire leading back to the coach. Hopefully you can identify which wire is causing the significant drain on the battery- the see what is disconnected by that wire.
If the coach wires are not the issue, something in the Mercedes electronics -
If no significant current draw, either a weak battery or something that intermittently draws significant power. Both of these seem less likely and harder to trace down...

I have hehlped two friends address this issue on their “SOB” Motorhomes with battery terminal cut-offs. In one case, where the chassis battery is “hidden”, we used a cut-off with remote activation.

As to what is “significant current” - a 100 ma continuous load would drain about 2.4 amp-hours per day, or over 30 amp-hours in two weeks. Would require some form of charging ~every two weeks. I would expect something more like <20 ma continuous load.

FYI
Jim

[Bill Davis]

Originally Posted by JLeising

Similar on our 2012 MBS. Not sure what may have changed on the MBS side since 2012, but no such problem on ours.

My thought- pull a battery cable off the chassis battery and put an amp meter between the battery terminal and the cable. Pulling the cable off the battery terminal eliminates any question wrt an alternative ground through the coach, or related. If significant current flowing, I would first start disconnecting any wire leading back to the coach. Hopefully you can identify which wire is causing the significant drain on the battery- the see what is disconnected by that wire.
If the coach wires are not the issue, something in the Mercedes electronics -
If no significant current draw, either a weak battery or something that intermittently draws significant power. Both of these seem less likely and harder to trace down...

I have hehlped two friends address this issue on their “SOB” Motorhomes with battery terminal cut-offs. In one case, where the chassis battery is “hidden”, we used a cut-off with remote activation.

As to what is “significant current” - a 100 ma continuous load would drain about 2.4 amp-hours per day, or over 30 amp-hours in two weeks. Would require some form of charging ~every two weeks. I would expect something more like <20 ma continuous load.

FYI
Jim

On modern vehicles with multiple computers it may take 10 minutes or so for all of them to go into sleep mode when following above procedure. Just be aware of that when checking for a current draw. Don’t be fooled by the initial reading. It should drop off after the 10 or so minutes and what’s left is your draw.

[Bill Davis]

Originally Posted by caswelld

Yup...if you store your motorhome out in the elements with solar it will keep ahead of all the parasitic electrical draw MB designed into the chassis.

But we store ours in a garage, so it looks like I need a battery disconnect.

How about just putting a battery tender on it. That’s what I do with my Harley in the winter.

[bclemens]

Originally Posted by caswelld

Well, I pulled the battery disconnect at the accelerator and saw an "Important" sticker. It said to allow 10 minutes after engine shut down for the emission control system to do its thing before pulling the disconnect. I guess this is a common thing to do in MB world.

I'll find out in a few weeks it worked.

Brian, just wondering if your guys pull that cable on all your MB chassis while they're waiting to enter production? How long do the MB chassis typically set around before production?


Dave

We do not....but we have a guy that keeps the batteries charged. I don't know that we have many issues with the MB batteries. Then when in production we plug them in every step of the way.

I will say, mice love the MB wiring harness. I am told they use peanut oil to pull the wiring.

[caswelld]

Originally Posted by Bill Davis

How about just putting a battery tender on it. That’s what I do with my Harley in the winter.

Great idea but my extension cord would be about 5 miles long, no electric in the storage garage we rent.

[halla]

Thats a long cord. Lol

Can you pull the batteries and charge at home? I know its not ideal but cheaper than destroying the batteries.

[kp5692958]

Originally Posted by caswelld

For the 3rd time now the chassis battery is dead after sitting for just 2 weeks. Nothing is plugged into the DC outlet. I don't see any parasitic drain on the system. I'm glad the house batteries were available!

I mentioned this to the tech at the dealer and he said MB has had a lot of issues with this. He said they start the MBs on their lot every week.

Any known fix, or is it off to Mercedes?



Dave

We have a 2018 isata 3 that had the same issue. Took into MB and they replaced the battery and have not had a problem in 10 months. We keep getting a diagnostic error code but the console did not display an engine light. Hope this helps