coach battery woes


We have a problem with our coach batteries draining quickly and not charging while driving (They will charge on shore power and on the generator.). We experienced several electrical grimlins which lead up to our present situation. First symptom was a dead starting battery - we replaced it have had no issues. Second was a warm fridge and tripped circuit breaker, followed by dim lighting and finally the charging issues. Running with the generator or being plugged into shore power solves all problems electrical. The fridge works on LP meaning the 12v to board is working. The AC, microwave and fridge will work on both shore power and the generator. Autozone checked the two 6 volt coach batteries and saw no problem. They are original and probably should be changed. I am reluctant to tear into the electrics too much but simply do not have the money for a $100/hr RV shop to perform troubleshooting.

Are there any ideas on how to simplify the troubleshooting process? If so, perhaps we could narrow down the fix and thus afford the professional repair.

Thanks in advance for all your help. It's cold up here and Michigan and I have lots of time to work on the RV.
coach battery woes

Has anyone checked the alternator on the engine? Usually, when the engine does not charge, that is the culpert. There may be a inline fuse to look for if the alternator checks out. I don't sell MH's, but that is a general rule of thumb.

Good luck and welcome to the forum.
coach battery woes

If you leave the coach plugged into shore power for several days and then unplug it, will everything work properly on the batteries for any period of time? Did you separate the two batteries and load test them? The AC and microwave should not work on the coach batteries unless you have a big inverter. I am guessing you have one or two bad batteries. Hope so, that will probably be the least expensive fix. Krazee


Senior Member
coach battery woes

Does the starting battery charge while driving? If so, the alternator is probably ok.

Get a charging system meter (Radio Shack has a little one for $5) and see what the voltage is across the coach batteries while the engine is running; this will tell you if it is being charged. For grins, it would be interesting to compare this value to that across the starting battery (assuming that it does charge) and even to that value across the coach batteries when you are plugged in or on generator.

If it is not charging, then it could be a loose or dirty connection, a popped fuze or circuit breaker, or other blown component. You could try tracing connections between the starting battery and the coach battery to find where you lose the charge voltage.
coach battery woes

Thank you for the quick replies and questions. I'll try to answer them in series.

Does the starting battery charge when driving down the road? Yes.

Do the coach batteries hold a charge for any length of time? Not very well. They drain very fasy. Less than one hours time.

Did Autozone connect the batteries together when they performed a load test? No.

I took them to the store in the back of our toad and we tested them one at a time. They man said they passed which surprised me. I figured he would try and sell me two batteries at the very least, but he sent me away to look elsewhere.

The AC and microwave do not work on the coach batteries, only the shore and generator. Sorry if the post was unclear.

I have not taken any readings across the batteries yet, Perhaps this weekend if the weather allows.

Thanks again for all your help. Keep the brainstorms coming!
coach battery woes

To quote you: "The AC and microwave do not work on the coach batteries, only the shore and generator."

The AC and Microwave work on 120v of electricty, NOT 12v off the batteries unless you have one heck of an inverter.

Not sure what is draining your batteries.
coach battery woes

Well if the batteries are good and are draining that fast there must be quite an arc when you connect them back in service due to the amperage that evidently is being drawn. And if there isn't an appliance doing that it has to be a short. And it's a big one that I would think is getting quite warm. I think I would get a second test on the batteries.
coach battery woes

Thanks again for all the tips. I'll try and get an amp measurement across the batteries this weekend. I'll also verify the charging with engine running and generator off, engine off and generator running, and engine off - generator off- shore power on. Any other suggestions?
coach battery woes

I did check the water in the batteries when we tested them. They were low but not out. We topped them off with distilled water and tested them with Autozone's draw-down test cart. He said they tested fine. I am not a battery expert, but assumed he would sell me batteries at the first hint of failure. He did not. We did not test the batteries in series - only as individual units on a 6 volt system.
coach battery woes

If it does turn out to be the batteries, what brand would you recommend? The OEMs look like Trojans but have no external markings.
I'm assuming a like for like replacement would be the best path. Any suggestions?
coach battery woes

OK here are some more clues. The weather was unseasonably warm today so I got a headstart on the spring troubleshooting. The rig has been unplugged for weeks, last started in November, circuit breakers in the off position. Found the batteries not able to turn over the engine even with the coach assist. The generator would not start either.

Caoch #1 Coach #2 Series Chassis bat Comments
4.22v 2.42v 6.63v 11.21v Eng off, Gen off, Shore off
4.61v 6.27v 10.90v 10.91v Eng off, Gen off, Shore on
6.04v 7.05v 13.87v 13.09v Eng on, Gen off, Shore off
6.77v 6.39v 13.61v 13.63v Eng on, Gen on, Shore off
5.06v 6.58v 12.40v 12.55v Eng off, Gen on, Shore off

Ran the rig for about an hour (jumped it), turned off the engine but left the generator running for another hour. Tried to start the engine but the generator quit and the engine would not start. It's to dark to take "as left readings" now. I'll look at again in the morning.

On the bright side, I did get the rear sway bar bushings replaced, one was missing and one was a mess. Not too difficult - just messy.


Senior Member
coach battery woes

Battery problems can be any 1 or a combination of: battery, charger or circuitry attached.

From your measurements, it looks almost like the only charging circuit which may be working is the Engine alternator. If your inverter/converter were working correctly, I would think the series voltage should be over 13v if charging with shore power only. If the generator was providing a good charge, the series voltage should also be over 13v with generator only. Of course, in many cases, the generator does not charge batteries directly, but feeds the inverter/converter, so I would first check that out further.

It sounds like you have a converter, not an inverter/charger. It does seem like it is providing 12 volts from shore or the generator to run the 12v parts of your unit, so it may not be completely bad, but may not be providing the higher voltage necessary for a good charge. If practical, with the shore power plugged in, compare the output from the charger (as close as you can get to it) to the value across the batteries to see whether it is a supply problem or a transmission problem. If the voltages are essentially the same, then investigate what value the charger SHOULD be putting out. I think it should be more than 13v, but am only guessing.

Next I'd check to see if the batteries can be charged. If you have a known good external charger, you could try unhooking all the battery cables from the batteries (mark them so you can put them back right :) ) and charge all the batteries. Since an electrical check (Auto-zone) did not seem to indicate any problem, I might invest a buck or 3 into a liquid battery tester (hygrometer?) and test every cell. If it passed these tests, I'd take them to a different battery store than the one you went to before (if practical) and have them re-load tested. You might want to see if you can get a desulfator/battery maintainer, so that when these problems are resolved, you can keep the batteries in good shape while in storage. If this is not practical, possibly a solar powered unit might do the job.

Once you determine that there are no problems with the battery or charger, it get really interesting...
coach battery woes

Thanks Hertig, Krazeehorse, and Grandview for the advice:

Next clue: The converter, a Progessive Dynamics Intelli-Power 9000, shows 13.6 volts at the output with the coach plugged into shore power. According to their website, that's where it should be. Next up, the charging voltage. Film at eleven.

The batteries this morning were not charged after being plugged into shore power overnight. So much for luck....
coach battery woes


Thanks to you guys and your wisdom, we think we have found the problem. When tracing the converter wiring back to the batteries we found a loose lug on the common ground to the furthest coach battery. We crimped and tightened the fittings and presto! everything works! Must be good advice and clean living! Thanks for all the help!

I have to say, this experience must be what the founders had in mind when they created this website. Thanks you for your patience and experience - hopefully I can pass it on down the line somewhere further along the journey. :)

Thanks again!
coach battery woes

M'.d,javascript:insertsmilie(' :cool: ')
Cool :cool: Even tho the problem is fixed, I wanted to propose 2 suggestions for other folks looking to shortcut the expensive problem finding process. Get a $7~10.00 "VOLTAGE HOUND" (it will find voltage "leaks"/shorts/loose grounds by running them down any given wire or at a connection panel and making an increasing noise when approaching bare wire, loose or corroded connection. Get an "electric clamp meter"(to id the wire that is discharging your batteries by amperage flow)and using it simply by turning unit on and using the trigger to place the clamps around the wire. I suspect if most of the rv repair shops used accepted procedures for trouble-shooting and resolving problems their bill would be significantly less. Seems like more of the rv'rs are becoming the can-do types :cool: , Two Dogs


Senior Member
coach battery woes

Will that 'voltage hound' trace 12v dc wires? If so, do you have more descriptive information? I can't find any trace of it on the internet.