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Old 11-15-2018, 10:43 AM   #1
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Dead Battery on Mercedes Isata 3

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
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Old 11-15-2018, 04:16 PM   #2
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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.
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Old 11-15-2018, 08:44 PM   #3
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Quote:
Originally Posted by caswelld View Post
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.
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Old 11-15-2018, 09:55 PM   #4
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Quote:
Originally Posted by bclemens View Post
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.
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Old 11-16-2018, 08:53 AM   #5
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I do know a lot of the new vehicles have tons of electronics. The Ram has two chassis batteries.
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Old 11-16-2018, 11:37 AM   #6
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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.
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Old 11-16-2018, 04:36 PM   #7
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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.
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Old 11-17-2018, 06:53 AM   #8
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"It didn't matter if I disconnected the battery even...weird."


If the battery dies when disconnected its a BATTERY problem.
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Old 11-17-2018, 08:48 AM   #9
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Wonít help

Quote:
Originally Posted by caswelld View Post
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.
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Old 11-17-2018, 09:29 AM   #10
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"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....
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