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Old 12-03-2021, 03:05 PM   #1
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Dead Coach Batteries

I had a senior moment, and did not turn off my batteries when in storage. The engine battery worked fine, but the coach batteries were dead cold. My surprise was that I could not start the generator on the engine battery. It seems illogical to me that when you really need the generator, it won't start. So my RV is in front of my house on an extension cord for shore power and charging.

So, is there some trick to starting the generator when the house batteries are dead? All these years I thought the generator was connected to the engine battery, but never had to test that assumption.

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Old 12-03-2021, 03:10 PM   #2
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In order:


Try BOOST SWITCH


If that isn't enough, start the big engine and let the alternator bring it up enough to either start the generator just from house battery bank OR using boost switch to add chassis batteries to the mix.
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Old 12-03-2021, 04:02 PM   #3
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I think the boost switch only works to start the engine with the engine battery is dead, not the other way around. I tried this morning, just in case. I also drove it 60 miles at high RPM, but that did not charge the house batteries enough to start the generator. Bad design!
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Old 12-03-2021, 04:13 PM   #4
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Quote:
Originally Posted by RVsteve View Post
I think the boost switch only works to start the engine with the engine battery is dead, not the other way around. I tried this morning, just in case. I also drove it 60 miles at high RPM, but that did not charge the house batteries enough to start the generator. Bad design!
You may already be aware of this, but will post anyway. When lead acid batteries are completely discharged, they have to be replaced. So not surprised that generator will not start, probably never will no matter how much you try to charge them. Hope they were on their final days and you got good use out of them. Many other posts on what to replace with... you have lot of options flooded, AGM, 6v vs. 12v, etc. even lithium.
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Old 12-03-2021, 04:29 PM   #5
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You inverter may have a low battery cutoff. You can use a car charger to bring them back up (if they didn’t go too low) to the point the inverter/charger will work.
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Old 12-03-2021, 04:49 PM   #6
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I have been told for years that house batteries and marine batteries are designed to completely discharge. My house batts are new, so should be in good shape. Whatever, I should know after the RV is on shore power overnight. It if will not hold a charge, then I go back to Interstate.
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Old 12-03-2021, 04:59 PM   #7
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Quote:
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I think the boost switch only works to start the engine with the engine battery is dead, not the other way around. I tried this morning, just in case. I also drove it 60 miles at high RPM, but that did not charge the house batteries enough to start the generator. Bad design!

Suspect you have some other issue.


The boost switch just COMBINES BATTERY BANKS. Yes, if the "signal" is from the depleted battery, it will not work.


But, if your alternator, battery isolator and house bank are all in working order, 60 miles will ABSOLUTELY charge the house bank enough that your converter or inverter/charger will take over.


Lastly, can you 100% discharge the batteries-- sure, they are yours. Will that SIGNIFICANTLY shorten their life-- SURE. Would love to see your reference to that level of discharge not significantly affecting battery life.
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Old 12-03-2021, 05:11 PM   #8
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Driving should have brought up the house batteries.
Since it didn't, that leads to a bad isolation solenoid. The isolation solenoid sends charge to the house batteries from the charging chassis batteries. It isolates them if no charging.

The isolation solenoid also serves as the boost solenoid. The fact that it didn't work for boost is another indication that it's bad.

As far as shore power charging, if the batteries are very low and you have an inverter/charger ( most likely in a 40 ft MH ), the charger will not kick in.
Driving it some would have brought them up but not if the solenoid is bad.

Deep cycle batteries can be run down without damage to 10.6 volts, not zero volts, but that doesn't mean they are shot, just wonder. Get them charged to save them.
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Old 12-03-2021, 07:19 PM   #9
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So try this.

If you have a switch to disconnect the house batteries, disconnect them. Then turn the boost switch on.
If you donít have such a switch, then remove the connection cables from the house batteries.

The logic is that the dead house battery bank is a huge voltage sink when you try to merge the dead bank with a charged battery.

You may be lucky if you can do this, and the wiring to the generator is still in the circuit when you merge the batteries with the house bank disconnected.

This is not wild theory. A coach owner with a medium size LiPo bank, completely discharged his chassis battery. No problem, right. When he merged the LiPo and the chassis battery, the LiPo bank blew a 400 amp fuse. The point is the dead battery will draw a great deal of current from the charged one when merged. More current then even a running engine with alternator can provide.
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Old 12-03-2021, 08:32 PM   #10
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Quote:
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I have been told for years that house batteries and marine batteries are designed to completely discharge. My house batts are new, so should be in good shape. Whatever, I should know after the RV is on shore power overnight. It if will not hold a charge, then I go back to Interstate.
I would not follow that advice. No lead acid battery should be discharged to zero it permanently damages it or can kill it completely. Deep cycle and AGM can be safely discharged further but not zero. To get longest life (number of cycles) check battery specs and see what manufacturer recommends as the lowest safe discharge % or voltage. There is a lot of info online about this.
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Old 12-05-2021, 05:52 PM   #11
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My seven year old chassis batteries were dying while in storage. One day I wanted to start the rig and couldn't. Shimmed the batter boost switch so that the decent, well charged chassis batteries could partially charge and start the motor - no go.

I got the jumper cables out of my car, went to my battery compartment in the rig's basement and simply jumped from the chassis to the coach batteries. Immediately when into the cab and started right up.

Moral: Jumper cables worked far better than playing with the boost switch.

And to address the dead coach batteries - yes, you can do the same operation - jump to the chassis batteries and let them charge up a bit...

Sure - folks will say there is something wrong with my boost solenoid - after all, the rig is 13 years old. Who cares? I have jumper cables.

P.S. I have new chassis batteries now.
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Old 12-05-2021, 06:45 PM   #12
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Quote:
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My seven year old chassis batteries were dying while in storage. One day I wanted to start the rig and couldn't. Shimmed the batter boost switch so that the decent, well charged chassis batteries could partially charge and start the motor - no go.

I got the jumper cables out of my car, went to my battery compartment in the rig's basement and simply jumped from the chassis to the coach batteries. Immediately when into the cab and started right up.

Moral: Jumper cables worked far better than playing with the boost switch.

And to address the dead coach batteries - yes, you can do the same operation - jump to the chassis batteries and let them charge up a bit...

Sure - folks will say there is something wrong with my boost solenoid - after all, the rig is 13 years old. Who cares? I have jumper cables.

P.S. I have new chassis batteries now.
With your boost solenoid being bad, there's a good chance that the chassis battery were not automaticly getting a charge from the well charged house batteries.

That solenoid handles the chassis to house charging, when the engine is running AND probably the house to chassis charging when on shore power.
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