Nexus class C battery issue

I don't like paralleled 12's. They just don't seem to play well together like 6's in series. I'd have to do mods on our coach to add another 12 or a pair of 6's, but for what we do, one 12 is enough. Previous coach had paralleled 12's and nothing but trouble. Went to one 12 and (again for our kind of use, we are not boondockers) we've been OK. I like the paralleled 12's for the idea that maybe if one fails the other can finish the trip, but it never worked out for me.

Charging your battery will take more than a couple of hours.

Depending on your converter, it could take much more than 2 hours. Use your multimeter to check the charging voltage while the battery is still discharged. A good charger will charge at over 14 volts, probably closer to 14.5v, and still take many hours. If its only being charged at 13.5v, it could take a long time.

When you're plugged in, the little battery voltage meter (I assume you're referring to one with three or four little lights on a tank level/information panel sort of setup, but it's true for any voltmeter) will show the charge voltage, not the battery resting voltage, since that's the voltage being applied. For little lights, this equates to "fully charged" practically all the time.

If you're starting the generator while still plugged into shore power, you are getting a sizable portion of the power to crank the generator from the converter rather than the batteries. My Onan 4K requires somewhere around 100A to crank, so a 40A converter can supply almost half that and make for a noticeably less severe load on the batteries. That's not very useful when you actually need to run the generator (i.e. when you don't have shore power available).

Charging the batteries fully or nearly fully from the converter when they're quite discharged might require a day or so...for sure more than a couple hours. As others have said, it's not unlikely that the batteries need replacing. Lead acid batteries do not take at all kindly to sitting in a discharged state.

Sully2 wrote:
They are just getting a surface charge and thats just enough to fire up the genset.

Well that's not exactly what "surface charge" is but you can't fully charge a dead battery in just a couple of hours.

It is likely that the batteries have been left dead for too long and now are shot.

They need to be fully charged and then tested.....but "boiling" a battery is neither necessary nor good.

Not being able to give up the charge that a battery has is one sign that it is worn out.

I agree with most of what has already been posted. Your batteries are 4 years old and have one or more bad cells. Any battery wth a bad cell can be charged until Christmas but when a load is applied, in this case starting the genny they immediately go flat. A Hydrometer will confirm this.

The so called dual purpose batteries found in many RV's are more prone to this than true deep cycles. My 2012 nexus Class C came with two group 27 Interstate, pure deep cycles and they lasted 5 years. They showed weak at the end of their life when I tested with the Hydrometer but there were no bad cells - they were all equally low.

The converters on most RV's are between 35 and 55 amps {probably the case with your larger C}, and while they do in fact charge they are not dedicated chargers. The solution is to simply confirm my theory with a Hydrometer and then replace both with pure deep cycles. I got mine at Batteries Plus for $100 a piece.

I also replaced the engine battery as it was 5/6 years old {the chassis on my 2012 is in fact a 2011}, and should now be done buying batteries for the next 3 - 5 years which is about right given regular use and proper maintenance.

:C

I would venture to guess that plugging in your motorhome and allowing the converter to charge the house batteries will only give you a minimum charge, perhaps just sufficient to start the generator, and if the batteries are too dead, or not salvageable, repeating the same process will only result in the same results you are getting. If your batteries are more than three years old, consider changing to 6 volt Trojan batteries, or at least, charging your batteries over 24 hours with a real charger, not a trickle charger or converter.

Charge meter reads battery voltage as a measure of charge state, but not capacity. If a large part of the battery plate area is damaged (sulfation, drying out) they will come to full voltage quickly, and run down quickly, because the capacity has been lost.

My experience is that with only occasional use, long periods of storage, and at best casual maintenance, the RV/Marine flooded cell batteries most often used in C's will last 2-3 years. They'll do a lot better in continuous service with proper multi-stage chargers, but long periods of storage and self-discharge, or continuous charging at RV converter float voltages will damage them or shorten their life.

The other thing that can happen, if you have two 12V batteries in parallel and one gets a shorted cell, it will quickly bring down the battery that is good. The charging and monitoring systems will see only the good battery. I have a pair in parallel, and find that I have to disconnect the two to learn much of anything about the actual condition of either.

I am on my third pair, at 11 years, ready for a fourth, or a better battery technology, or better use and storage conditions.

You will note that these usually sold with 24-month or shorter warranties. That is a realistic service life without exceptional care. You can do better by using actual deep cycle batteries, usually a pair of 6-volt.

Sounds like bad batteries. Have you checked acid level in batteries??

They are just getting a surface charge and thats just enough to fire up the genset. Disconnect the batteries and use a stand along charger on them ( it??) and let them roll and "boil". Each one of both. When finished disconnect it all....let sit 24 hrs and then check the voltage in each with a VOM. Then you have the truth to what you have.