baffled by "emergency start" button use

EDIT - I realize I used the wrong terms for the batteries which made it extra confusing.  It was 2AM and there was no coffee.  Updated my post.

On a recent trip I have managed to encounter all of these conditions and in none of them did the emergency start button on my dashboard do anything.
- dead vehicle (chassis) battery, fully charged house battery
- somewhat dead vehicle battery (headlights shine but not enough to crank over), fully charged house battery
- fully charged vehicle battery, dead house battery - possibly not ENTIRELY drained but too low for lights or steps.  A fan seemed to run weakly. 

In each case I held down the emergency start button (it's a spring-loaded rocker switch) and either pressed the button for generator start or turned the key in the ignition.  I hear clicking.

First off - which emergency is the switch for - dead vehicle battery or dead house battery?

How do I begin troubleshooting?  It's supposed to get me out of one of those conditions, right?

For dead vehicle battery, I got a jump from a really nice couple from Tennessee and driving around charged the battery. 

My house battery did not charge while I was driving.  I couldn't start my generator to see if running it would charge the house battery.  Is shore power the only way to recharge the house battery?  (I also have solar panels but they only trickle charge and they were suuuuuppppper dirty so basically no help with dead/extremely low house battery.)

Any recommendations on neat upgrades that might save me from myself?

Hold down the emergency start button for a minute or two and let the dead battery get a bit of a charge before trying to start the vehicle.

For clarification, let's use the terms chassis battery and house battery; You can see the respective definitions in our Glossary of RV terms (button in the menu above).

In the event of a dead chassis battery that won't crank/start your engine, using the emergency start button connects the house battery(ies) to the chassis battery, and the combined battery power hopefully cranks/starts the engine. But, if the house battery is also dead, you're out of luck.

On many RVs, the house battery does not get charged when driving, and is only charged when you're plugged into shore power.

The chassis battery may or may not be charged when plugged into shore power, depending on how your RV is wired.

If your house battery is dead, pressing the emergency start button for more than a few seconds merely discharges the chassis battery.

    Effectively what the "emergency switch" does is place all batteries into a parallel mode to give you the most 12 volt power possible.  You must hold it down for it to have any effect.  However if you have a short in one of your batteries, it is likely that could negate the ability to allow power to the system.  I have used it from charged house to low chassis, and vice versa.  As I said, if working properly, it ties both battery banks together to provide the most power available.

Ed

Not sure of why your vehicle battery is dead but the reason the emergency switch is not working is probably because the battery mode solenoid is not working.  If it was it would allow the house battery to jump to the vehicle battery through the emergency switch.  You may have other problems that are causing the vehicle battery not to charge (alternator, etc) but if your house battery is charged via shore power but not by the vehicle alternator the battery mode solenoid could be the problem.  Hope this doesn't confuse more than help.

Bill

The Emergency start switch, sometimes called the BOOST button "Jumpers" the house and chassis batteries together.  THis can be useful if ONE of the batteries are down.  However not if BOTH sets of batteries are down or if someone jumpered them together.

I like to hold it for 20-30 seconds.. then wait 20-30 seconds, then press and start.

On many RVs, the house battery does not get charged when driving, and is only charged when you're plugged into shore power.

The chassis battery may or may not be charged when plugged into shore power, depending on how your RV is wired.

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Tom, did you get those two backwards when you typed the message?  To the best of my knowledge, just about every motorhome charges the house batteries from the engine alternator, though not always very effectively. Only some of them, however, charge the chassis battery from the house system when on shore power.

Gary--I think You're right.  On mine about 20 seconds after I start the engine there is a "clunk" and the house lights get a little brighter.

Yes, Gary is right, and the "clunk" you hear is usually the same solenoid closing that the "E-Start/Boost" switch controls, connecting the two battery sets in parallel. Sometimes it's operated by the ignition switch turning on, and sometimes it's wired through an oil pressure sensor so it only kicks in when the engine is actually running, while other RV's have a "BIRD" (Bi-Directional Isolator Relay Delay) device that monitors the alternator output to control the switching. That would account for the delay before you hear it "clunk".

Mea cupla. Not reversed per se, but not correct. For clarification ...

Our current Monaco charges the house battery, but only after the chassis battery has reached some predefined level of charge. The chassis batteries are not charged when on shore power.

I was thinking that our prior gas coach didn't charge the house batteries from the engine alternator. But, on reflection, I recall that it had a diode isolator that allowed both chassis and house batteries to be charged while driving. It also had a charge line from the converter to the chassis battery, so the latter  was charged (sometimes overcharged) while on shore power.

Thanks for the responses.  The key seems to be not holding the button down and waiting.  (Coincidentally "not waiting long enough" seems to be the root of most of my computer related issues too).  Understanding that I basically get one massive battery from all batteries in parallel helps a lot - basically, it's like I've connected jumper cables between my vehicle and house batteries.

My vehicle (chassis) battery died because I left the lights on.  If I open the driver door I get a warning beep but if I kill the engine and get up & exit through the house door on the side of the vehicle I don't get the warning beep.  I'm ashamed to say this has happened more than once.  I also once drained the vehicle battery not realizing that being plugged into shore power did not charge that battery, and we had the radio on all night. 

Right now my RV is parked at home and the house battery is dead but vehicle battery is fully charged.  I should be able to start the generator with the emergency start button, right?  I can't wait to go try it out!

Maybe NOT, the boost switch is usually powered by the house batteries, so if they're dead that switch won't work. If you know where that solenoid is located you can jumper it from the chassis battery, but I'd have the engine running when you do.

You may also have dirty contacts inside your battery isolator solenoid.  It can be tricky because it'll "clunk" when you hold down the boost switch, but the dirty contacts won't allow any current from one set of batteries to the other.  If you have someone toggle the boost switch for you, you can find the isolator solenoid and test it.  It's USUALLY under the entrance steps near the house batteries, but not guaranteed.  When I replaced my defective isolator solenoid it cost me $15 on Amazon!  Good luck

Charlie 5320 said:

Maybe NOT, the boost switch is usually powered by the house batteries, so if they're dead that switch won't work. If you know where that solenoid is located you can jumper it from the chassis battery, but I'd have the engine running when you do.

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I had that problem on our previous coach. To prevent it from happening again, I fed the boost switch from both battery sources through isolation diodes. It's on my "Roundtoit" list for this coach too...