Monaco Won't Start. Batteries acting weird

[mexicanpiloto13]

This is a strange one and has me guessing. My 1998 Monaco Coach with Cummins 350 has always started. But I recently noticed the alternator was charging almost 16 amps and took it into the shop. I thought it too excessive. They first checked the Lifetime agm batteries, (about 3 years old) then checked the charge the alternator was putting out at the isolator, he said. It was normal and the panel gauge was found to be bad. I drove the unit home and parked it, and that's the last time it ever started. Batteries have about 12.8 volts measuring at the terminal, but the panel just "clicks" when you try and start it and all the warning lights go off. When I connect the house battery to the engine battery by using the toggle on the panel, same thing, just clicks, the warning lights on the panel dim. the generator won't even start, which I believe is started using the coach batteries. I was going to try a charge but it appears the batteries are pretty well charged up. I am wondering if the RV shop left a wire off, or threw a disconnect switch or something to cause this first-time problem. They are closed for the weekend. Any thoughts. the lights in the coach work fine, and looks like they have a good charge. My panel inside says the batteries have at leas 3/4 charge both about 12.8 volts. Something is not getting through.
Dead in the Water in Arizona. thanks

[YC_1]

You need to put a voltmeter on the battery posts, dead center of the posts and then have someone turn the key. If the voltage holds above 11 volts or so then move the negative lead of the voltmeter to the frame. Scratch a shiny place. Then place the voltmeter dead center of the negative lead and have someone turn the key. This will tell you if you have a ground path problem. You should not get any voltage from the negative lead (center of the post) to the ground.

Be very careful to NOT disturb any battery cables. Don't go tugging and pulling because it is nice to find the actual problem and not accidently fix the problem.

If you get zero volts during this test then leave the negative test lead on the shiny frame place and move the voltmeter positive to the center of the positive post and have someone turn the key again. If the voltage stays above 11 volts then move the positive lead of the meter to someplace beyond the battery post. You may find a battery shut off switch post for example or some solenoid nearby. Do this test again. If the voltage is way down just beyond the battery post then you have a bad connection at the battery.

At some point moving towards the battery starting solenoid you should encounter a low voltage situation while turning the key of course. Once you find that first low voltage point you can cheerfully work your way back cleaning and tightening all of the connections.

Of course you can just shotgun it and take every connection off and clean them.
This is a common problem and good maintenance will help prevent this. A dremel tool with a round sanding drum is great for shining up connections. Keep sparks away from the batteries of course and do use safety goggles.

Twelve volts has very little "push" or force and has a difficult time going through any slight corrosion or bad connection. In the old days of 6 volt systems it was even worse. Going to 12 volts from 6 volts gives four times the power. Many aircraft use 24 volts. Our telephone system land lines use -48 volts. Don't worry about the math on the increase in power.

And when we went from 6 volts the wiring size was reduced. Go figure.

[Bruce_Brown]

12.6 volts isn't really considered fully charged, so you might be on to something with them being disconnected as you drove home. 13.2 volts is considered fully charged.

[mexicanpiloto13]

Thanks so much for all the helpful advice on our Monaco that won't start. Yes, to the one poster, I did mean 16 volts, not amps. I did the check of putting the headlights on and trying to start the engine. They didn't dim, but blinked rapidly along with the blinking panel lights. Good tip also on the front/rear start switch in the engine bay but I drove it home so switch was engaged to front. I'm starting to think the engine cut off switch and coach switch for batteries were turned off when the batteries were cleaned, and perhaps the engine switch is still off. I can't reach it where its parked. Amazingly, the invertor works and generates full AC power 120 volts, 60 cycles. But generator won't start, nor will it extend from the front of the coach. It just "clicks" as well. I carefully measured volts on all the battery posts and got about 12.6 volts and also measured on the battery cables, also checked continuity on all that and fine. I'll let you know what I find out when I call the RV place tomorrow for help. Again, I always wait until I have no other answer and then post a question on RV.net, and so many great folks are quick to respond with their ideas. I sure do appreciate it.

[Twomed]

Do you have the Front/Rear start switch in the engine bay? Techs (and owners too) often select Rear Start and forget to reset...oops no start.

Hope it's that easy.

[wa8yxm]

First you said 16 amps. That is very LOW current from an alternator which can deliver easily 100 amps or more Did you mean 16 VOLTS (I think you did)

Now... Batteries... Full charge per the meter but no start just a click.. I've had that happen two different ways
Method #1 (Failure 1.2.3 not sure about 4) turns out the body builder put the wrong kind of TERMINAL on teh positive lead and corrosion was causing a high resistance.. I'd turn the key everythign lit up normal. turn to START and everything died.. Cleand 'em up and VAROOM.. Finally changed the terminal to a proper battery terminal with a short pigtail and did an advanced job there.. The original ring terminals are HIs-I said HIS--That is HIS-tory.

Finally I had to put in a new battery.. (That's when I changed the termainal)

Last failure (last April) CLICK. just a sharp CLICK not a loud THUNK but a Sharp Click.

IN my main Chassis fuse box (On a workhorse this MAY be front and center under the hood) there is a relay marked STARTER. this is a pilot relay.. I removed it. cleaned the contacts and replaced VAROOM.

[rgatijnet1]

Turn your headlights on and while watching them turn the start switch and see if the headlights dim. If they do it is almost certainly a connection/corrosion issue. If the light stay bright, it could be a starter solenoid issue.

[gbopp]

Clean and tighten your battery terminals. A little corrosion (even if you can't see it) can cause problems.

[wanderingaimles]

Good voltage , but lose power when load is applied is ofter a corrosion issue. Check at the battery first and work back. Since the genny wouldn't start either, battery connection would be my first stop.