AGM coach batteries won't charge

[icw2gotra]

We have a 3-yr old Winnebago Trend class C motor home, came with 2 NAPA AGM coach batteries. We live in southern Arizona. This RV has not seen much use, driven 4500 miles in 3 years and was stored on a lot the first 2, then parked at our house past 12 months, where it's usually plugged in to a dedicated 30-amp circuit that an electrician added to our outdoor main electrical panel. I realized on our last short outing that the coach batteries are not holding a charge at all. No power if the engine or generator is not running or if unplugged from shore powere. Battery levels look like this on the monitor panel:
Engine off, coach plugged in, coach battery in 'disconnect' mode:
Chassis bat = 12.3v House bat = 13.2v
Unplug from shore power and the monitor panel goes dead.
Turn on engine and monitor panel levels are:
Chassis bat = 14.1v House bat = 14.1v
Did I do anything wrong in keeping the RV plugged in to shore power the last several months, while it was just parked? Or is this what happens to a battery after 3 years in southern AZ? Is there any way to revive these AGM batteries?

[Morich]

Several points on this may need more checking. Firs is that when there is charging of any type, the voltage readings will only be what the charger is putting out and not mean anything on what the battery condition might be.
Your readings on both start and coach seem reasonable but not really meaningful but may help to understand.
So when unplugged, things are all dark and that often means the coach battery id dead. Plugged in, the coach batteries are being charged but not the start battery, making your readings as expected because a fully charged battery never get above the 12.X range but the coach is higher because it is receiving a charge. In other words you are seeing what is coming from the charge system but no telling about what the coach battery has.
Then when the engine runs, the car alternator is puts out 14+ and you can see that change as the engine speeds up or slows down but the tricky thing is that when the RV engine is started there is a solenoid which automatically connects both strings together as a way to add some charge back to the coach batteries as we move to a different site
making you see the high reading on both as it is just the alternator voltage.
Final result is that what you see is the chargers and not the actual batteries alone and when using them it seems dead!
So what killed things? Maybe just time and temp or it could be as simple as corroded cables but I lean toward dead, so I would want to take them for testing at a shop like auto parts stores where they often do it free.
AGM do last better but they do still get some gassing and do get some damage if not watched.

[Winterbagoal]

It does look like morich is correct, and they might be toast, based on the numbers you're seeing in various situations. I'm pretty sure my One Place monitor panel is dead when the batteries are also dead. I'll check that and get back to you.
Ideally, the best way to check is what morich suggested, but you could do it yourself.
Plug in to shore and leave it overnight. Then take a "before" picture of your coach battery cabling configuration, and then turn the battery enable/disable switch off, then disconnect the cables carefully, and use a digital multi-meter to check their state of charge.
If disabling the battery switch does completely cut them off from any draws, you don't have to diconnect the cables before you check them.

[Winterbagoal]

Originally Posted by Winterbagoal

It does look like morich is correct, and they might be toast, based on the numbers you're seeing in various situations. I'm pretty sure my One Place monitor panel is dead when the batteries are also dead. I'll check that and get back to you.
Ideally, the best way to check is what morich suggested, but you could do it yourself.
Plug in to shore and leave it overnight. Then take a "before" picture of your coach battery cabling configuration, and then turn the battery enable/disable switch off, then disconnect the cables carefully, and use a digital multi-meter to check their state of charge.
If disabling the battery switch does completely cut them off from any draws, you don't have to diconnect the cables before you check them.

EDIT: Batteries disabled (or dead), RV not plugged into shore power, no power to One Place monitor panel. Confirmed.

[Morich]

I think Al and I are looking at the same thing on the batteries but testing a different way, so you can choose how to go with testing.
What I think we see is a set of batteries that don't look like they have good voltage, but only when that voltage is from some form of charger, Shore power or alternator but if we cut off that charging and disconnect the battery cable, we can wait a few hours and the batteries should have at least 12 volts. This can be as simple as taking the negative cable which goes to ground off the battery post as it only takes cutting the circuit which removing the ground cable is usually the less congested and easier to remove. Then waiting several hours will let the battery chemicals all settle out and if we don't see good 12+, we know that the charge did not hold.
What I think you are dealing with is called "surface charge" and does get weird at times.
My favorite surface charge story is this!
Think of a battery like a barrel of water and the charge as a bit of black ink poured in the hole at the top. When we first look at the water, it can look really black and we think the whole barrel is that color but if we wait a few hours after we stop pouring ink in, we might look and find we don't see much color at all as it has spread and settled in the whole barrel, rather than being just at the top where we look.
I like the simple ideas!

[icw2gotra]

Thanks for the excellent feedback and analysis! I don't have any way to disconnect the battery cables - these batteries are held in a tray underneath the chassis and the whole unit has to be lowered, with the use of one or two jacks, just to get access to the terminals. I'm told this is why Winnebago chose to use AGMs on this model, to eliminate the need for maintenance/monitoring - which I'm not set up to do anyway. If the battery 'level' is just reflecting its input charge source and the battery itself can't maintain any charge, they must be toast.

So here's the question I got once we arrived at the conclusion that we have dead coach batteries:

- What do we need coach batteries for anyway? We never boondock; we're always on shore power or engine power or generator.

- If we didn't replace them what is the long-term consequence of needing to power the coach, when not plugged in, from the chassis alternator - always (?) trying to charge the battery; and same goes for the generator (Onan gasoline 2500W I think)?

[Morich]

Originally Posted by icw2gotra

Thanks for the excellent feedback and analysis! I don't have any way to disconnect the battery cables - these batteries are held in a tray underneath the chassis and the whole unit has to be lowered, with the use of one or two jacks, just to get access to the terminals. I'm told this is why Winnebago chose to use AGMs on this model, to eliminate the need for maintenance/monitoring - which I'm not set up to do anyway. If the battery 'level' is just reflecting its input charge source and the battery itself can't maintain any charge, they must be toast.

So here's the question I got once we arrived at the conclusion that we have dead coach batteries:

- What do we need coach batteries for anyway? We never boondock; we're always on shore power or engine power or generator.

- If we didn't replace them what is the long-term consequence of needing to power the coach, when not plugged in, from the chassis alternator - always (?) trying to charge the battery; and same goes for the generator (Onan gasoline 2500W I think)?

Good questions and how we each see the answer will vary but some info from my point of view. Be very slow and careful when deciding the batteries are no good as they tend to confuse us and testing by a pro may save a fair amount of money or let us use some that we might think too far gone as AGM batteries do tend to last better.
But what happens if we leave them and can't get much use?
When driving, do you stop for lunch , etc. and may want to wash hands? No water pressure if the engine is not started. Maybe okay, maybe not.
Depends on each RV design but some use the coach batteries to start the generator and weak batteries will probably eventually go totally bad to possibly get to the point they are shorted and will reduce the power of the start battey when tied together like when engine is running. The two strings are tied together when the engine starts as a way to get some charge put back into the coach battery after we have run it down some but when we tie a bad battery to a good one, it "sucks" power out of the good. As long as the engine alternator is running it just works a bit harder but that has a bit of risk to it.
Depends on luck and how we deal with things but this is one that I might mention. We often have a switch on the radio to power it from the start or coach battery but when we park, we forget, leave it on the start battery and use the radio to run the start battery down. Start battery doesn't charge off shore or generator if we have not made some provisions which are not often built in RV. Some do, some don't. But we can wind up with a dead start battery and that is when we have an AUX switch on the dash to let us do a semi-automatic "jump start" to get going. Not going to help if the coach AND start battery are dead/weak.
I hate spending money but on the other hand, I have already spent so much on the RV, that I would really not want to lose the full experience with bad coach batteries. We often pull to the roadside for lunch or dinner and don't crank the genset (noise!) and then use the bathroom and wash hands, etc. before hitting the road again. More important when dark and we need lights inside to eat.
No wrong answers but just different views at times?

[icw2gotra]

Thank you, some of those situations came to mind when I was trying to answer the question, and there are many more that I didn't think of due to lack of experience. Personally I don't want to risk not having that built-in power when you need it - to start the generator, to start the engine if you forget and leave the keys in 'acc' mode overnight, or to make it so you *don't have to* start up either one and still have lights and TV :-)

[Pianotuna]

No. Leave the panel charging.

[Pianotuna]

Yes. Over charging kills most battery types.

[jbrattain]

My AGM NAPA batteries were doing the same thing recently. Turns out the water was seriously low. Added distilled water, batteries returned to normal performance.

[jerichorick]

Originally Posted by jbrattain

My AGM NAPA batteries were doing the same thing recently. Turns out the water was seriously low. Added distilled water, batteries returned to normal performance.

I think you have standard batteries. AGM batteries don't take water.

[jerichorick]

Originally Posted by icw2gotra

We have a 3-yr old Winnebago Trend class C motor home, came with 2 NAPA AGM coach batteries. We live in southern Arizona. This RV has not seen much use, driven 4500 miles in 3 years and was stored on a lot the first 2, then parked at our house past 12 months, where it's usually plugged in to a dedicated 30-amp circuit that an electrician added to our outdoor main electrical panel. I realized on our last short outing that the coach batteries are not holding a charge at all. No power if the engine or generator is not running or if unplugged from shore powere. Battery levels look like this on the monitor panel:
Engine off, coach plugged in, coach battery in 'disconnect' mode:
Chassis bat = 12.3v House bat = 13.2v
Unplug from shore power and the monitor panel goes dead.
Turn on engine and monitor panel levels are:
Chassis bat = 14.1v House bat = 14.1v
Did I do anything wrong in keeping the RV plugged in to shore power the last several months, while it was just parked? Or is this what happens to a battery after 3 years in southern AZ? Is there any way to revive these AGM batteries?

I suggest that you pull the Hot lead off your batteries with the charger off. Test and see what the voltage reading is.

[thataway4]

It is quite possible that your batteries are shot. Unfortunately you are going to have to pull them out--even if it means crawling under, unbolting, using a dolly jack or similar device to pull them. This is necessary to access the cables, and to fully charge the batteries and load test time.

Some converters will over charge batteries--the better ones have a "smart" charger which will only replace a small amount of current as it is lost. Many of the older or cheaper ones just give a constant current to the battery and do not taper off when the battery is fully charged. There are two ways around this--one is a charge wizard which attaches to the converter you have. (A converter basically is 40 to 50 amps to provide power when charged into the mains power or running of the generator, and powers the 12 volt system: lights, refer solenoids or compressors, TV sets, radio and amps etc. A true 3 or 4 stage smart charger gives the battery a bulk, adsorption and float phase, which will eventually charge the battery fully and keep it at it best state of charge. You can sometimes revive a damaged battery by using a pulse charger. (or a pulse with a smart charger) such as the PP-12-L PowerPulse 12-Volt Battery Maintainer. I have seen some batteries resurrected using this technology.

The house battery acts as sort of a buffer between the converter (mains power) and the alternator (when vehicle engine is running). I would not try and run the unit without batteries in place. You may want to see what "parasitic drains are present". That is radio memories, etc which use a small amount of power. I disconnect the chassis battery/engine battery if I am not using it, and every month of so, put a small 6 amp smart charger on the battery for 24 hours. I have gotten as much as 8 years service with two group 31's starting an 8.3 Liter diesel and a 10 KW Onan Diesel Generator. Doing the disconnected when not in use and then charging regularly.

[MadMaxWinny]

There is a great deal of good advice here for you. The bottom line is that your monitor is not a useful way to check the conditions of the batteries. For deep cycle AGMs, you need a voltmeter. A "full" and rested (no load) battery should read close to 12.8-12.9v when in good condition. Below 12.5v is a tired battery with "some" life left, and below 12.2v, the party is over. Starting batteries (flooded or AGM) need to be load tested at a shop.

[jbrattain]

Originally Posted by jerichorick

I think you have standard batteries. AGM batteries don't take water.

Sorry, brain fart, I meant to say NAPA deep-cycle.

[RTrider]

While my wife was in the hospital and recovering, we had a couple of months we were not in your MH and during that time I went to pick up something out of the unit and ran the generator for a while. On the way out the door, I forgot to hit the disconnects for the engine and house batteries. The unit is not plugged in. The next time I went to the unit, the batteries were so dead the the steps wouldn't even extend. I finally got enough charge in (jumper cables from the car) to start the engine and brought it to my house where I could plug in. Surprisingly, the engine battery more or less recovered. The 4 AGM house batteries did not. Within a hour of disconnecting power they showed 9 to 10 volts. After replacement, I haven't made that mistake again. $$$

[jerichorick]

Originally Posted by jbrattain

Sorry, brain fart, I meant to say NAPA deep-cycle.

LOL. Both can be deep cycle. Wet cells need watering. Absorbent Glass Mat don't and can't be.

[jerichorick]

icw2gotra go to a automotive shop like Pep Boy's and have them pull and test your batteries.

[Goodspike]

Originally Posted by thataway4

Some converters will over charge batteries--the better ones have a "smart" charger which will only replace a small amount of current as it is lost.

I'd not really worried about that in the past, but I don't tend to stay connected to power very long--more than 20 hours.

But couldn't you use the battery disconnect after being connected to power X hours, when you think your batteries have fully charged? I've never tried that, but I assume all the 12 volt stuff would still work.