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Old 01-17-2014, 12:33 PM   #1
Join Date: Aug 2013
Location: Western Washington
Posts: 58
Battery Question(s)

1. Are all 3 of my batteries (2 coach and 1 engine) wired in parallel – all together?
2. When I use 12 volt power in the coach, am I drawing voltage off the engine battery along with the coach’s batteries?
3. If so – if I’m not careful – I could kill all 3 batteries and not be able to start the vehicle.(?)

I’m still a newbe going through the learning curve. I have a 2013 Forester, c-class. My multimedia center is in the dash board, so I wanted to know if it was drawing off the engine battery like a normal vehicle radio – or if it was connected to the coach batteries. Doing what I thought would be a good test, I disconnected the engine battery to see if the multimedia station would still turn on. (Under normal conditions when you open the driver or passenger door, the parking lights and running lights turn on.) To my surprise, when I opened the driver’s door, the parking lights and running lights came on. And when I turned the ignition key to the “On” position the dash lights came on. I wasn’t expecting that because I thought I would have killed the vehicle’s normal power by disconnecting the engine battery. Out of curiosity, with the engine battery still disconnected I turned the coach’s battery disconnect to the “Off” position. Doing that I lost all 12 volt power to the coach, but still had power in the driver’s compartment.

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Old 01-17-2014, 01:41 PM   #2
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Join Date: Jul 2010
Location: Desert SW - Arizona
Posts: 5,887
This is the way it is in my Georgetown Motorhome

In general terms

1. Yes the two coach batteries are in parallel if they are both 12 volts.
The engine battery is only one so yes it is hooked up to the engine charger in parallel.
It also can be hooked up to your coach batteries if you have a emergency switch in the drivers seat.

When driving your engine charging system charges all batteries including the coach one.

If your engine battery goes dead while parked. You still have generator to charge your house batteries. If then your engine battery is dead you can hit the emergency switch and it will add house batteries to your engine so you can start your engine.

2012 Georgetown XL - 378TS 49,000 miles
(2013 - 98 days) (2014 - 117 days) (2015 - 67 days) (2016 - 115 days)
USAF Retired - MSgt

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Old 01-17-2014, 02:58 PM   #3
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Join Date: Oct 2009
Location: South Eastern PA
Posts: 19,827
Additionally, there is a reverse current relay that will prevent "house draw" from killing the motor starting battery.

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
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