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Old 10-21-2018, 01:36 PM   #1
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Brand: Thor Motor Coach
Model: Siesta 24ST
State: Maryland
Posts: 13
THOR #3964
2018 Thor Siesta 24ST chassis battery problem

After a nearly 3 month trip south to escape the cold months we returned to MD and parked our new coach for a few weeks. After just about 2 weeks I hopped in the coach, engaged the "use/store" switch to "use", looked at the "Vegatouch" panel and noticed that the chassis battery was below 12 and she wouldn't start. I wasn't smart enough to note the actual battery levels (I do now) but a charge to the chassis battery of about 10 minutes and she started.

I always ensure that the "use/store" switch is set to "store" before leaving the coach. The microwave clock off is a good indication that at least the house batteries are disconnected with the switch is in store.

I've taken the coach to a MB dealer a few times now and they can't find the problem, other than to note that they pointed to a cable connected to the chassis battery that in their opinion shouldn't be there.

Our coach has the "Summit" package with all those bells and whistles. Part of the Summit pkg is a solar panel and controller, but after leaving the dealer I realized that the controller display was showing an error message, so at this point the solar panel is not a solution if I leave the switch to "use." Frustrating to say the least, not knowing whether the coach will start after sitting for a couple weeks... Any other 2018 Thor Siesta / Synergy / Citation owners having chassis battery problems?
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Old 10-21-2018, 02:46 PM   #2
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Brand: Thor Motor Coach
Model: Palazzo 33.3 34'bunkhouse
State: Alabama
Posts: 2,063
THOR #4735
the Chassis battery(s) should really have no need for constant trickle charging, even when in storage for long periods, as it simply is a starting battery, not one that has, or should have, any type of 'phantom' unknown draws while just sitting.
What might the 'other' cable to this battery be for? Probably for the 'Aux' or 'Emergency Start' switch, to tie in the Chassis and House batteries when either are low, like a set of jumper cables.

If the batteries are falling, I imagine you have left something on, that draws from the Chassis battery(s), such as a radio or video system, or similar, that you sometimes want to use even when you don't have the engine cranked, or have to leave the key in the 'on' or 'accessory' position.

as for the Microwave - it does not use 12v power, so the 'Use/Store' switch actually has nothing to do with it, THOUGH, the switch probably DOES disable the INVERTER, which is what powers the microwave, a residential fridge, if you have one, and maybe other outlets within the coach.

The Use/Store switch simply is an easy way to remove all lights and other 12v house items from the batteries, but not necessarily every 12v device, as C02, Propane, and Smoke detectors will always be 'live', even with the switch in 'Store' position.

For solar, the panel usually attaches to a solar Controller, then directly to the battery(s), though I imagine that it's for the House battery(s), not the Chassis. And, whether the switch is in 'Store', or 'Use', won't impact that.

While this is generally how most RVs work, yours can have some 'extras' that may tilt the scales one way or the other, but most likely not too much. Some factories do things 'this' way, while others may do it 'that' way...

I suggest that you simply have a phantom draw on your Chassis battery(s). You could test this by removing the NEG cable from the Chassis battery(s), and check back several weeks and see if the level is any different. If not, you have a draw to find. If it is then lower, you may have a bad battery.
Or drive to most any parts store which can load test the battery(s)...
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Old 10-21-2018, 03:27 PM   #3
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Brand: Thor Motor Coach
Model: Siesta 24ST
State: Maryland
Posts: 13
THOR #3964
Thanks for your comments Turnerfam. MB confirmed that there is no "Emergency" switch to engage the house batteries to boost the chassis battery. With the key removed and the "use/store" switch in store, nothing is apparently on. RE disconnecting the negative lead from the chassis battery, on our coach it's under a panel in the cabin in front of the driver's seat, so not easy to routinely access. Will poke around further, thanks again...
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Old 10-21-2018, 05:13 PM   #4
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Brand: Thor Motor Coach
Model: Siesta 24SR
State: Arizona
Posts: 37
THOR #1894
In the operators manual it says to disconnect the chassis battery if storing 3 weeks or longer. MB says there is an extra wire on the battery? Could be drawing more current than the normal phantom current draw. I left mine disconnected for 6 months last year, and when I connected it back up the Sprinter started right up.

From the manual pages 118-119
If you park the vehicle for more than
three weeks:
connect the batteries to a trickle charger or
disconnect the vehicle's starter battery or
switch off the electrical system using the battery
main switch (Y page 118) and
disconnect the vehicle's auxiliary battery
Otherwise, you need to check the battery's condition
of charge every 3 weeks, since standby
power consumption can drain the battery. If the
battery voltage is lower than 12.2 V, the battery
must be charged. Otherwise, the battery may be
damaged by exhaustive discharging.

Here's a link for a copy of the manual, I like the pdf because you can easily search for info.

https://www.mbvans.com/sprinter/owne.../owner-manuals


Steve
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Old 10-21-2018, 06:22 PM   #5
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Brand: Thor Motor Coach
Model: Siesta 24ST
State: Maryland
Posts: 13
THOR #3964
Thanks Steve, I forgot to mention that previously I had a 2016 Thor Siesta 24SR and I could leave that coach for maybe 8 weeks and it always cranked over like it was yesterday... Same storage location, same pattern of use, so I was surprised at the difference ...
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Old 10-21-2018, 06:51 PM   #6
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Brand: Thor Motor Coach
Model: Siesta 24SR
State: Arizona
Posts: 37
THOR #1894
you wrote:
"I've taken the coach to a MB dealer a few times now and they can't find the problem, other than to note that they pointed to a cable connected to the chassis battery that in their opinion shouldn't be there."

Can you trace that wire, or maybe put an ammeter on it to see if that is drawing anything substantial?
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Old 10-21-2018, 06:57 PM   #7
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Brand: Thor Motor Coach
Model: Siesta 24ST
State: Maryland
Posts: 13
THOR #3964
Not something I'm willing to try, but I might ask an electrician friend to take a look... As I recall, it was a large wire, nearly the size of a battery cable.
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