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Old 10-28-2019, 10:10 PM   #1
JMF
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Brand: Thor Motor Coach
Model: Siesta SJ
State: North Carolina
Posts: 35
THOR #16303
Thor Siesta Mercedes Chassis Battery drain

We have just replaced our AGM Battery (80Ah) with a brand new one, since the old one was discharging within 6 days and appeared to drop charge under a small load.

We charged the new battery fully and then tested every day to see whether it was maintaining its charge. The main house switch is off and there doesn't appear to be any other load on the vehicle.

Here's the result: We are losing about 0.5V every day. It started at 12.8V and is down to 12.4V after 6 days (52%).

Has anyone else had this problem and resolved it? I've researched this on the web - seems that some people resolve it by using a Trickle Charger from the House Batteries, but I'd prefer to find out what the source of the drain is.

Any ideas?
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Old 10-28-2019, 10:17 PM   #2
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Brand: Still Looking
Model: Tiffin Wayfarer 24 BW
State: New York
Posts: 12,811
THOR #8860
Why not throw a battery disconnect switch into the mix, and see if it helps?
This is what I did with mine...

Okay: I ended up putting two on the battery bank. I wanted to completely isolate them.

http://www.thorforums.com/forums/att...1&d=1572301064
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Old 10-29-2019, 12:23 AM   #3
JMF
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Brand: Thor Motor Coach
Model: Siesta SJ
State: North Carolina
Posts: 35
THOR #16303
Quote:
Originally Posted by Bob Denman View Post
Why not throw a battery disconnect switch into the mix, and see if it helps?
This is what I did with mine...

Okay: I ended up putting two on the battery bank. I wanted to completely isolate them.

http://www.thorforums.com/forums/att...1&d=1572301064


We can disconnect the chassis battery by pulling the plug by the gas pedal. That fixes the drain when storing the MH.

The main switch is off for the house. But there shouldnít be a big drain on the starter battery when.all systems are switched off.
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Old 10-29-2019, 04:03 AM   #4
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Brand: Thor Motor Coach
Model: Synergy
State: Arizona
Posts: 18
THOR #12461
I have a 2018 Thor Synergy on a 3500 Mercedes chassis. When the motorhome is not in use, I store it in a covered storage area without access to 110 V. If I pull in to storage with the battery fully charged, i.e. 13.2 volts, it will take roughly 5 to 6 days in storage and the battery will be below 12 volts. My only way to charge it has been to start the coach Onan generator and charge the chassis battery with a small 6 amp charger. This of course takes propane, time, much patience and adds lots of hours to the generator. After following some of the forums, I have ordered a 18 W solar panel/trickle battery charger today from Amazon. I live in southern Arizona so I have lots of sun to charge the battery with. The afternoon sun shines in on the front of the cab even though it is undercover and it will provide adequate sunlight on the solar panel to keep this battery charged. I had never thought about the recommendation of putting in a couple of knife switches that was mentioned above; thatís not a bad idea either. After owning this rig for about 17 months, Iíve found that this parasitic drain is common, and did not surprise the Mercedes service advisor when I ask him about it. I guess itís just something that we will have to live with, be that through adding some sort of trickle charger while the coach sets idol, or put on the knife switches and disconnect the power totally. I suppose this is a small price to pay for, in my opinion, an excellent chassis, particularly this Mercedes diesel.
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Old 10-29-2019, 12:23 PM   #5
JMF
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Brand: Thor Motor Coach
Model: Siesta SJ
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THOR #16303
Hey Bob, Did you have a chassis battery drain and if so, did it fix the problem ?
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Old 10-29-2019, 01:11 PM   #6
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Model: Tiffin Wayfarer 24 BW
State: New York
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THOR #8860
I did...
Based upon my experience with our Outlaw: I felt it was easier to just completely isolate the batteries.
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