This weekend my chassis batteries lost all charge. I parked on Friday night and when I turned the ignition Sunday morning to ON I had no dash light indicators; tried the headlights and nothing. I was running the generator the entire time so the coach battery was fine.

The batteries had always fired the starter with no hesitation, ever. Alternator puts out 13.2-5.

I checked for a voltage leak and showed 0.
I checked for amp draw and got 0 at 10A setting and .5 at 200ma setting.
I put a load battery tester on and it showed that the batteries were good.

What am I missing here?

Now that I have charged them when I disconnect the chassis batteries positive cable the lights still work but when the batteries were dead the lights didn't work - so I guess I'm just stupid because this doesn't make sense to me.

Alternator output voltage will depend on the load encountered. If the battery's low, the voltage will be lower. 13.2 VDC is, to me, a bit low.

This sounds like you may have encountered a shorted cell, due to the sudden arise of the issue. Have you measured the voltage of the chassis battery disconnected?

I measured the chassis/engine batteries today after 24 hours of being parked and everything off.

The reading was 12.5 volts.
I again checked for amp draw and this time I got a reading of 0.

So it appears that nothing externally is drawing them down and the 12.5 reading isn't great but they are not dead either. The only thing that I did different when they went dead was run the generator nonstop and I can't imagine that that had anything to do with them going dead. The alternator has always been in the area of 13.2-5 at idle on both chassis and coach battery banks whenever I've checked.

I guess I could attempt to check each cell to be sure.
Could my readings be off because I did not check each battery separately (I left the parallel cable connected)?

I would give them a good long charge and let them sit for a day. Then test them with a hydrometer, DVM, load tester and conductance meter. Costco or Sams, as well as several chain auto parts stores use the Midtronics conductance tester, which I like. Harbor freight has reasonably priced load testers, and most auto parts stores will test your battery with one.

I also like my Vector 1095 charger as it has both equalize and desulfate functions. Whenever someone screws up and allows a battery to discharge, I use it to desulfate after a full charge. The Midtronics shows a great improvement from the desulfating.

Does your coach have a diode isolator?

Yes, I do have a diode isolator.
That's an item that I thought might be suspect in this as well. I just don't know how to check this unit to see if it's operating properly. That's also the reason I mentioned the generator running because it is charging the coach battery and I thought that maybe it was draining the chassis batteries if the isolator was affected somehow.

My eyes are glazing over now.

My Breakaway had an odd arrangement in that the generator charged the coach batteries, but ran off the chassis battery. The replacement Honda has its own battery.

But I suspect your genset is diesel, and even with the same arrangement, would draw only on starting.

The more I think about this (comments not desired ), the more I tend to think your diode isolator is the culprit. Leakage with a bad diode can be considerable.

I don't think I'm going to be able to do too much about this for a few days. I'll have time to monitor the voltage and that's about it.

If I were to start the generator and then check to see if there is an amp draw while it's running would that indicate a problem with the isolator more than anything else?

I don't know the age of these batteries but they are NAPA commercial 8D's and last time I checked they were a little on the pricey side, so I'd rather not just run out and replace them until I have this nailed down as to why they deep sixed on me without warning.

And yes the genset is an Onan diesel, but it does use the coach battery to start not the chassis batteries.

quote:

Originally posted by Steve WI:
I put a load battery tester on and it showed that the batteries were good.

Ok, this means that you disconnected each battery and then performed a load test. But then I read further down, you stated

quote:

Originally posted by Steve WI:
Could my readings be off because I did not check each battery separately (I left the parallel cable connected)?

This is not how you would "Load Test Batteries"

To load test your batteries you must disconnect them and load each one. Leaving the cables hooked up will not give you a good reading.

Follow Bill H's advice about a long charge and then use a hydrometer. Great advice.

12.5 volts is a discharged battery.

If you have one battery going bad it will suck voltage away from the other batteries.

I suspect a diode leak too. You would need to check your batteries first. Yes, they are expensive. Don't change them unless they fail. In my area, if you remove your batteries and bring them to Napa they will charge them and then load test your batteries for you. YMMV...

When I first got my coach I knew better... Or at least I thought so. All of my interior lights were "House Batteries" and anything that was in and around the dashboard was "Engine Batteries"...

The saying goes "You don't know, what you don't know, until you know it" well, I now know that the 2 lights over the driver and passenger windows are on engine batteries. These two pocket lights ran down my starting batteries because I ass-u-me'd they were part of the house electrical system.

having same problem with my new coach batteries load tested all five , batteries dead next day .. what does a diode isolator look like .. 86 regency 57000 miles this is an on going struggle ....

quote:

Originally posted by robert and kimberly delucia:
having same problem with my new coach batteries load tested all five , batteries dead next day .. what does a diode isolator look like .. 86 regency 57000 miles this is an on going struggle ....

Did they go dead when connected or disconnected? I don't really like load testing of coach batteries. At least, not as done by the cheapie testers. Yes, I own one and use it for chassis batteries.

To load test a coach battery, I measure and calculate what load and time it will take to drop the battery down to 50% State of Charge over several hours. Then I set it up and set a timer. When the timer goes off, I disconnect, wait an hour, and record voltage. Then I wait 24 hours and read voltage again.

There should not be more than a tenth of a volt difference, and the voltage should correspond to about 50% on a chart from a reputable source. However, they do not always agree, dang it. I use the Trojan chart, but all of this is a Kierkegaardian leap of faith. At some point it is necessary to suspend disbelief and act on faith. But not an act of faith, as in Auto de Fé

I still recommend doing more than one type of test when there is a vexing problem, as I have seen this stuff drive sharp professionals crazy. The more testing you do, the more liable you are to find the problem. Time and again, a battery will test OK one way one day, and be weak the next. Time not only heals all wounds, but it wounds all heels and tells the tale on batteries.

went dead connected ..... coach batteries load tested with new tester from o riellys..had four coach bateries replaced with five? all positives to positives all neg to neg

HI Guys: I recently went through the "engine batteries are dead" and traced and traced and found a constant .5 volt draw. After a lot of investigation I found the switch for the electric actuated piston for the air operated steps has a bare wire and was grounding. So I had a constant draw on the batteries. Fixed the wire on the switch and that was the last of the mystery. The wires to your steps are hanging in the wind and subject to road debris and whatever else is kicked up. My search ran from the batteries to the electric panel to each relay and finally to the steps. You might look at that as one possible solution.
Tom

quote:

Originally posted by Bill N.Y.:
12.5 volts is a discharged battery.

quote:

Originally posted by bill h:
Huh? http://www.trojan-battery.com/Tech-Support/BatteryMaintenance/Testing.aspx

Well, you know that I know better then that.

I was trying to type this and I was looking up state of charge and I was thinking that it was around 75% - 80%. My next sentence was supposed to be something around the line of 1/4 discharged battery and the importance of a long charge. Then, my mechanic called in and Penske was on the line, this morning was payday (Thurs/Fri holiday) and I just got busy. Somehow, what I had highlighted from the Interstate website got deleted when I hit send. To much of a rush to recheck the post...

You know, it probably would be easier to just delete your post and edit mine... If only I knew someone who had that type of power.

Thanks for the head up Bill H we wouldn't want to give out bad advice.

We'll just call this a big old "Ooops!" and never speak of it again.