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Author Topic: Should I connect house and starting batteries together?  (Read 362 times)

lancefb

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Should I connect house and starting batteries together?
« on: November 25, 2017, 02:59:26 PM »
Is it a problem to connect both my batteries together? The house battery is a hybrid deep cell type while the starting battery is typical for that purpose. I don't have solar yet, so while dry camping, running down the house battery, I could recharge it by connecting it to the alternator. I was thinking of using a simple on/off switch to separate them as per my diagram. I would only turn on the connection when I needed a charge from the alternator, otherwise would be off.
Lance F. Barker
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1973 Dodge Beaver
Kona Kikapu mountain bike + bike trailer
Plumas County, CA

HappyWanderer

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Re: Should I connect house and starting batteries together?
« Reply #1 on: November 25, 2017, 03:13:54 PM »
They need to remain isolated. What would you do in the middle of nowhere with two dead batteries?

Are you sure that the house battery doesn't already charge from the alternator?
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lancefb

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Re: Should I connect house and starting batteries together?
« Reply #2 on: November 25, 2017, 04:05:32 PM »
They need to remain isolated. What would you do in the middle of nowhere with two dead batteries?

Are you sure that the house battery doesn't already charge from the alternator?

There actually is an existing connection from the starting battery to the house battery in the form of a 4AWG (or so) that I took off because there appears to be no solenoid or isolator between them. THAT would lead to 2 dead batteries. I'm suggesting keeping the wire in place but adding a switch to isolate them. But the other question is if charging a starting battery and a hybrid deep cell house battery at the same time from the alternator can lead to an early death of the house battery.

Lance F. Barker
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1973 Dodge Beaver
Kona Kikapu mountain bike + bike trailer
Plumas County, CA

SeilerBird

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Re: Should I connect house and starting batteries together?
« Reply #3 on: November 25, 2017, 04:19:03 PM »
That switch is built into many RVs already. Look around your dash for an emergency start switch.
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John From Detroit

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Re: Should I connect house and starting batteries together?
« Reply #4 on: November 25, 2017, 04:27:26 PM »
I have seen it done. The problem is if you do it. and run them down.. YOu have NO way of startin the RV save an external jump. and the starting battery is generally Toast.

With a proper isolator the Chassis battery can Jump start the gerator or the house jump start the chassis engine
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lancefb

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Re: Should I connect house and starting batteries together?
« Reply #5 on: November 25, 2017, 04:37:33 PM »
That switch is built into many RVs already. Look around your dash for an emergency start switch.

Definitely not!  ;D This is a 1973 Dodge Beaver.
Lance F. Barker
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1973 Dodge Beaver
Kona Kikapu mountain bike + bike trailer
Plumas County, CA

HappyWanderer

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Re: Should I connect house and starting batteries together?
« Reply #6 on: November 25, 2017, 05:30:29 PM »
I would add an isolator instead of a switch, which will prevent the house battery from draining the chassis battery. I don't see an issue with the mixed battery types, that's very common.
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Gary RV_Wizard

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Re: Should I connect house and starting batteries together?
« Reply #7 on: November 26, 2017, 11:13:40 AM »
As John explained, the drawback is that excessive use of house power also drains the engine start battery, resulting in a no-start for the coach. The whole reason for having two batteries to begin with is the isolation between them. Otherwise you could just install a bigger chassis battery. Of course, wiring them in parallel is effectively making one big battery.

You can manually switch the connection as you  stated, but human nature is to forget that when things get a bit hectic and then comes the shocker the next day when the coach won't start. A simple battery disconnect relay avoids that nasty surprise. You can wire a relay so that +12v from the engine ignition switch activates it, providing charging to the house battery from the alternator.
« Last Edit: November 26, 2017, 11:17:51 AM by Gary RV_Wizard »
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Stephen S.

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Re: Should I connect house and starting batteries together?
« Reply #8 on: November 26, 2017, 01:12:46 PM »
My class C has a battery isolator, a one way circuit between the chasis and house batteries.

I run off the two house batteries while boondocking, then they get recharged when I start up the engine with the chassis battery.

Set up properly it all happens without any input from me. A switch on the dash bypasses the isolator so the house batteries can help start the RV if the chassis battery gets low.

Stephen S.
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